path: root/docs/manual/mod/mod_md.xml

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<modulesynopsis metafile="mod_md.xml.meta">
    
    <name>mod_md</name>
    <description>Managing domains across virtual hosts, certificate provisioning 
        via the ACME protocol
    </description>
    <status>Experimental</status>
    <sourcefile>mod_md.c</sourcefile>
    <identifier>md_module</identifier>
    <compatibility>Available in version 2.4.30 and later</compatibility>
    <summary>
        <p>
        This module manages common properties of domains for one or more virtual hosts. 
        Its serves two main purposes: for one, supervise/renew TLS certificates via the 
        ACME protocol (<a href="https://tools.ietf.org/html/rfc8555">RFC 8555</a>). 
        Certificates will be renewed by the module ahead of their expiration to account 
        for disruption in internet services. There are ways to monitor the status of all 
        certififcates managed this way and configurations that will run your own 
        notification commands on renewal, expiration and errors.
        </p><p>
        Second, mod_md offers an alternate OCSP Stapling implementation. This works with
        managed certificates as well as with certificates you configure yourself. OCSP
        Stapling is a necessary component for any https: site, influencing page load
        times and, depending on other setups, page availability. More in the
        stapling section below.
        </p><p>
        The default ACME Authority for managing certificates is 
        <a href="https://letsencrypt.org/">Let's Encrypt</a>, but it is possible 
        to configure another CA that supports the protocol.
        </p>
        
        <p>Simple configuration example:</p>
        
        <note><title>TLS in a VirtualHost context</title>
        <highlight language="config">
MDomain example.org

&lt;VirtualHost *:443&gt;
    ServerName example.org
    DocumentRoot htdocs/a

    SSLEngine on
    # no certificates specification
&lt;/VirtualHost&gt;
        </highlight>
        <p>
            This setup will, on server start, contact
            <a href="https://letsencrypt.org/">Let's Encrypt</a>
            to request a certificate for the domain. If Let's Encrypt can verify the ownership
            of the domain, the module will retrieve the certificate and its chain, store it
            in the local file system (see <directive module="mod_md">MDStoreDir</directive>)
            and provide it, on next restart, to <module>mod_ssl</module>.
        </p><p>
            This happens while the server is already running. All other hosts will continue
            to work as before. While a certificate is not available, requests for the managed
            domain will be answered with a '503 Service Unavailable'. 
        </p>
        </note>

        <note><title>Prerequisites</title>
        <p>
            This module requires <module>mod_watchdog</module> to be loaded as well.
        </p><p>
            Certificate sign-up and renewal with Let's Encrypt requires your server to be
            reachable on port 80 (http:) and/or port 443 (https:) from the public internet.
            (Unless your server is configured to use DNS for challenges - more on that under
             'wildcard certificates')  
        </p><p>
            The module will select from the methods offered by Let's Encrypt. Usually LE offers
            challenges on both ports and DNS and Apache chooses a method available.
        </p><p>
            To determine which one is available, the module looks at the ports
            Apache httpd listens on. If those include port 80, it assumes that the
            http: challenge (named http-01) is available. If the server listens
            on port 443, the https: challenge (named tls-alpn-01) is also added to
            the list. (And if <directive module="mod_md">MDChallengeDns01</directive> 
            is configured, the challenge dns-01 is added as well.) 
        </p><p>
            If your setup is not so straight forward, there are two methods available
            to influence this. First, look at <directive module="mod_md">MDPortMap</directive>
            if the server is behind a portmapper, such as a firewall. Second, you may
            override the module's guesswork completely by configuring
            <directive module="mod_md">MDCAChallenges</directive> directly.  
        </p>
        </note>

        <note><title>https: Challenges</title>
        <p>
            For domain verification via the TLS protocol `tls-alpn-01` is the name
            of the challenge type. It requires the Apache server to listen on port 443
            (see <directive module="mod_md">MDPortMap</directive> if you map that port
            to something else).
        </p><p>
            Let's Encrypt will open a TLS connection to Apache using the special indicator
            `acme-tls/1` (this indication part of TLS is called ALPN, therefore the name
            of the challenge. ALPN is also used by browsers to request a HTTP/2 connection).
        </p><p>
            As with the HTTP/2 protocol, to allow this, you configure:
        </p>
        <highlight language="config">
Protocols h2 http/1.1 acme-tls/1
        </highlight>
        <p>
            And the `tls-alpn-01` challenge type is available.
	</p>
        </note>

        <note><title>Wildcard Certificates</title>
        <p>
            Wildcard certificates are possible, but not straight-forward to use out of
            the box. Let's Encrypt requires the `dns-01` challenge verification 
            for those. No other is considered good enough.
        </p><p>
            The difficulty here is that Apache cannot do that on its own. As the name implies, `dns-01` 
            requires you to show some specific DNS records for your domain that contain 
            some challenge data. So you need to _write_ your domain's DNS records.
        </p><p>
            If you know how to do that, you can integrated this with mod_md. Let's 
            say you have a script for that in `/usr/bin/acme-setup-dns` you configure 
            Apache with:
        </p>
        <highlight language="config">
MDChallengeDns01 /usr/bin/acme-setup-dns
        </highlight>
        <p>
            and Apache will call this script when it needs to setup/teardown a DNS challenge 
            record for a domain. 
        </p><p>
            Assuming you want a certificate for `*.mydomain.com`, mod_md will call:
        </p>
        <highlight language="config">
/usr/bin/acme-setup-dns setup mydomain.com challenge-data
# this needs to remove all existing DNS TXT records for 
# _acme-challenge.mydomain.com and create a new one with 
# content "challenge-data"
        </highlight>
        <p>
            and afterwards it will call
        </p>
        <highlight language="config">
/usr/bin/acme-setup-dns teardown mydomain.com
# this needs to remove all existing DNS TXT records for 
# _acme-challenge.mydomain.com
        </highlight>
        </note>

        <note><title>Monitoring</title>
            <p>
                Apache has a standard module for monitoring: <module>mod_status</module>.
                mod_md contributes a section and makes monitoring your 
                domains easy.
            </p><p>
                You see all your MDs listed alphabetically, the domain names they contain, 
                an overall status, expiration times and specific settings. The settings 
                show your selection of renewal times (or the default), the CA that is used, 
                etc.
            </p><p>
                The 'Renewal' column will show activity and error descriptions for certificate 
                renewals. This should make life easier for people to find out if everything 
                is all right or what went wrong.
            </p><p>
                If there is an error with an MD it will be shown here as well. This let's 
                you assess problems without digging through your server logs.
            </p><p>
                There is also a new 'md-status' handler available to give you the MD information 
                from 'server-status' in JSON format. You configure it as
            </p>
            <highlight language="config">
&lt;Location "/md-status">
  SetHandler md-status
&lt;/Location>
            </highlight>
            <p>
                on your server. As with 'server-status' you will want to add 
                authorization for this. 
            </p><p>
                If you just want to check the JSON status of a specific domain, simply append 
                that to your status url:
            </p>
            <highlight language="config">
> curl https://&lt;yourhost>/md-status/another-domain.org
{
  "name": "another-domain.org",
  "domains": [
    "another-domain.org",
    "www.another-domain.org"
  ],
  ...
            </highlight>
            <p>
                This JSON status also shows a log of activities when domains are renewed:
            </p>
            <highlight language="config">
{
"when": "Wed, 19 Jun 2019 14:45:58 GMT",
"type": "progress", "detail": "The certificate for the managed domain has been renewed successfully and can be used. A graceful server restart now is recommended."
},{
"when": "Wed, 19 Jun 2019 14:45:58 GMT",
"type": "progress", "detail": "Retrieving certificate chain for test-901-003-1560955549.org"
},{
"when": "Wed, 19 Jun 2019 14:45:58 GMT",
"type": "progress", "detail": "Waiting for finalized order to become valid"
},{
"when": "Wed, 19 Jun 2019 14:45:50 GMT",
"type": "progress", "detail": "Submitting CSR to CA for test-901-003-1560955549.org"
},
...
            </highlight>
            <p>
                You will also find this information in the file `job.json` in your staging and, 
                when activated, domains directory. This allows you to inspect these at
                any later point in time as well. 
            </p><p>
                In addition, there is <directive module="mod_md">MDCertificateStatus</directive> which
                gives access to relevant certificate information in JSON format.
            </p>
        </note>

        <note><title>Stapling</title>
            <p>
                If you want to try the stapling in one Managed Domain alone at first,
                configure:
            </p>
            <highlight language="config">
&lt;MDomain mydomain.net>
  MDStapling on
&lt;/MDomain>            
            </highlight>
            <p>
                and use the 'server-status' and/or <directive module="mod_md">MDMessageCmd</directive> to see how it operates. You will
                see if Stapling information is there, how long it is valid, from where it came and
                when it will be refreshed.
            </p><p>
                If this all works to your satisfaction, you can switch it on for all your
                certificates or just your managed ones.
            </p><p>
                The existing stapling implementation by mod_ssl is used by many sites
                for years. There are two main differences between the mod_ssl and mod_md
                one:
            </p>
            <ol>
                <li>On demand vs. scheduled: mod_ssl retrieves the stapling information
                when it is requested, e.g. on a new connection. mod_md retrieves it
                right at server start and after 2/3rds of its lifetime.</li>
                <li>In memory vs. persisted: mod_ssl <em>can</em> persist this
                information, but most example configurations use a memory cache. mod_md
                always stores in the file system.</li>
            </ol>
            <p>
                If you are unlucky and restart your server during an outage of your CA's
                OCSP service, your users may no longer reach your sites. Without persistence
                your server cannot provide the client with the data and the client browser
                cannot get it as well, since the OCSP service is not responding. 
            </p><p>
                The implementation in mod_md will have peristed it, load it again after
                restart and have it available for incoming connections. A day or two before
                this information expires, it will renew it, making it able to copy with
                a long OCSP service downtime.
            </p><p>
                Due to backward compatibility, the existing implementation in mod_ssl could
                not be changed drastically. For example, mod_ssl is unable to add a dependency 
                to mod_watchdog without braking many existing installations (that do not load it).
            </p>
        </note>

    </summary>
    
    <directivesynopsis>
        <name>MDomain</name>
        <description>Define list of domain names that belong to one group.</description>
        <syntax>MDomain <var>dns-name</var> [ <var>other-dns-name</var>... ] [auto|manual]</syntax>
        <contextlist>
            <context>server config</context>
        </contextlist>
        
        <usage>
            <p>
                All the names in the list are managed as one Managed Domain (MD). 
                mod_md will request one single certificate that is valid for all these names. This
                directive uses the global settings (see other MD directives below). If you
                need specific settings for one MD, use
                the <directive module="mod_md" type="section">MDomainSet</directive>.
            </p><p>
                There are 2 additional settings that are necessary for a Managed Domain:
                a contact Email address (via <directive module="mod_md">MDContactEmail</directive> or <directive module="core">ServerAdmin</directive>)
                and <directive module="mod_md">MDCertificateAgreement</directive>.
                The mail address of <directive module="core">ServerAdmin</directive>
                is used to register at the CA (Let's Encrypt by default).
                The CA may use it to notify you about
                changes in its service or status of your certificates.
            </p><p>
                The second setting, <directive module="mod_md">MDCertificateAgreement</directive>, 
                should have the value "accepted". By specifying this, you confirm that your
                accept the Terms of Service of the CA. 
            </p>
            <example><title>Example</title>
                <highlight language="config">
MDContactEmail admin@example.org
MDCertificateAgreement accepted
MDomain example.org www.example.org

&lt;VirtualHost *:443&gt;
    ServerName example.org
    DocumentRoot htdocs/root

    SSLEngine on
&lt;/VirtualHost&gt;

&lt;VirtualHost *:443&gt;
    ServerName www.example.org
    DocumentRoot htdocs/www

    SSLEngine on
&lt;/VirtualHost&gt;
                </highlight>
            </example>
            <p>
                There are two special names that you may use in this directive: 'manual'
                and 'auto'. This determines if a Managed Domain shall have exactly the 
                name list as is configured ('manual') or offer more convenience. With 'auto'
                all names of a virtual host are added to a MD. Conveniently, 'auto' is also
                the default.
            </p>
            <example><title>Example</title>
                <highlight language="config">
MDomain example.org

&lt;VirtualHost *:443&gt;
    ServerName example.org
    ServerAlias www.example.org
    DocumentRoot htdocs/root

    SSLEngine on
&lt;/VirtualHost&gt;

MDomain example2.org auto

&lt;VirtualHost *:443&gt;
    ServerName example2.org
    ServerAlias www.example2.org
    ...
&lt;/VirtualHost&gt;
                </highlight>
            </example>
            <p>
                In this example, the domain 'www.example.org' is automatically added to
                the MD 'example.org'. Similarly for 'example2.org' where 'auto' is configured
                explicitly. Whenever you add more ServerAlias names to this
                virtual host, they will be added as well to the Managed Domain.
            </p><p>
                If you prefer to explicitly declare all the domain names, use 'manual' mode. 
                An error will be logged if the names do not match with the expected ones.
            </p>
        </usage>
    </directivesynopsis>

    <directivesynopsis type="section" idtype="section">
        <name>MDomainSet</name>
        <description>Container for directives applied to the same managed domains.</description>
        <syntax>&lt;MDomainSet <var>dns-name</var> [ <var>other-dns-name</var>... ]&gt;...&lt;/MDomainSet&gt;</syntax>
        <contextlist>
            <context>server config</context>
        </contextlist>
        
        <usage>
            <p>
                This is the directive <directive module="mod_md">MDomain</directive>
                with the added possibility to add setting just for this MD. In fact,
                you may also use "&lt;MDomain ..>" as a shortcut.
            </p>
            <p>
                This allows you to configure an MD that uses another Certificate Authority,
                have other renewal requirements, etc.
            </p>
            <example><title>Example</title>
                <highlight language="config">
&lt;MDomain sandbox.example.org&gt;
    MDCertificateAuthority   https://someotherca.com/ACME
&lt;/MDomain&gt;
                </highlight>
            </example>
        <p>
            A common use case is to configure https: requirements separately for
            your domains.
        </p>
            <example><title>Example</title>
                <highlight language="config">
&lt;MDomain example.org&gt;
    MDRequireHttps temporary
&lt;/MDomain&gt;
                </highlight>
            </example>
        </usage>
    </directivesynopsis>

    <directivesynopsis>
        <name>MDCertificateAgreement</name>
        <description>You confirm that you accepted the Terms of Service of the Certificate
        Authority.</description>
        <syntax>MDCertificateAgreement accepted</syntax>
        <contextlist>
            <context>server config</context>
        </contextlist>
        <usage>
            <p>When you use mod_md to obtain a certificate, you become a customer of the CA (e.g. Let's Encrypt). That means you need to read and agree to their Terms of Service, 
            so that you understand what they offer and what they might exclude or require from you. 
            mod_md cannot, by itself, agree to such a thing. 
            </p>
        </usage>
    </directivesynopsis>

    <directivesynopsis>
        <name>MDCertificateAuthority</name>
        <description>The URL of the ACME Certificate Authority service.</description>
        <syntax>MDCertificateAuthority <var>url</var></syntax>
        <default>MDCertificateAuthority https://acme-v02.api.letsencrypt.org/directory</default>
        <contextlist>
            <context>server config</context>
        </contextlist>
        <usage>
            <p>
                The URL where the CA offers its service.
            </p><p>
                Let's Encrypt offers, right now, four such URLs. Two for
                the own legacy version of the ACME protocol, commonly named ACMEv1.
                And two for the RFC 8555 version, named ACMEv2.
            </p><p>
                Each version has 2 endpoints, as their is a production endpoint and a
                "staging" endpoint for testing. The testing endpoint works the same, but will
                not give you certificates recognized by browsers. However, it also has
                very relaxed rate limits. This allows testing of the service repeatedly
                without you blocking yourself.
            </p>
            <example><title>LE Staging Setup</title>
                <highlight language="config">
MDCertificateAuthority https://acme-staging-v02.api.letsencrypt.org/directory
                </highlight>
            </example>
        </usage>
    </directivesynopsis>

    <directivesynopsis>
        <name>MDCertificateProtocol</name>
        <description>The protocol to use with the Certificate Authority.</description>
        <syntax>MDCertificateProtocol <var>protocol</var></syntax>
        <default>MDCertificateProtocol ACME</default>
        <contextlist>
            <context>server config</context>
        </contextlist>
        <usage>
            <p>
                Specifies the protocol to use. Currently, only <code>ACME</code> is supported.
            </p>
        </usage>
    </directivesynopsis>

    <directivesynopsis>
        <name>MDDriveMode</name>
        <description>former name of MDRenewMode.</description>
        <syntax>MDDriveMode always|auto|manual</syntax>
        <default>MDDriveMode auto</default>
        <contextlist>
            <context>server config</context>
        </contextlist>
        <usage>
            <p>This directive exists for backward compatibility as the old name for
            <directive module="mod_md">MDRenewMode</directive>.
            </p>
        </usage>
    </directivesynopsis>

    <directivesynopsis>
        <name>MDRenewMode</name>
        <description>Controls if certificates shall be renewed.</description>
        <syntax>MDRenewMode always|auto|manual</syntax>
        <default>MDRenewMode auto</default>
        <contextlist>
            <context>server config</context>
        </contextlist>
        <usage>
            <p>
                In the default 'auto' mode, the module will do what makes most sense
                of each Managed Domain. For a domain without any certificates, it will
                obtain them from the Certificate Authority. 
            </p>
            <p>
                However, if you have defined an MD that is not used by any of Apache's 
                VirtualHosts, it will not bother. And for MDs with static certificate
                files (see <directive module="mod_md">MDCertificateFile</directive>), 
                it assumes that you have your own source, and will not renew them either.
            </p>
            <p>
                You can override this default in either way. If you specify 'always',
                the module will renew certificates for an MD, regardless if the
                domains are in use or if there are static files.
            </p>
            <p>
                For the opposite effect, configure 'manual' and no renewal will
                be attempted.
            </p>
        </usage>
    </directivesynopsis>

    <directivesynopsis>
        <name>MDHttpProxy</name>
        <description>Define a proxy for outgoing connections.</description>
        <syntax>MDHttpProxy <var>url</var></syntax>
        <contextlist>
            <context>server config</context>
        </contextlist>
        <usage>
            <p>Use a http proxy to connect to the <directive module="mod_md">MDCertificateAuthority</directive>. Define this
            if your webserver can only reach the internet with a forward proxy.
            </p>
        </usage>
    </directivesynopsis>

    <directivesynopsis>
        <name>MDMember</name>
        <description>Additional hostname for the managed domain.</description>
        <syntax>MDMember <var>hostname</var></syntax>
        <contextlist>
            <context>server config</context>
        </contextlist>
        <usage>
            <p>
            Instead of listing all dns names on the same line, you may use
            <directive>MDMember</directive> to add such names
            to a managed domain.
            </p>
            <example><title>Example</title>
                <highlight language="config">
&lt;MDomain example.org&gt;
    MDMember www.example.org
    MDMember mail.example.org
&lt;/MDomain&gt;
                </highlight>
            </example>
            <p>
               If you use it in the global context, outside a specific MD, you can only
               specify one value, 'auto' or 'manual' as the default for all other MDs. See
               <directive module="mod_md">MDomain</directive> for a
               description of these special values.
            </p>
        </usage>
    </directivesynopsis>

    <directivesynopsis>
        <name>MDMembers</name>
        <description>Control if the alias domain names are automatically added.</description>
        <syntax>MDMembers auto|manual</syntax>
        <default>MDMembers auto</default>
        <contextlist>
            <context>server config</context>
        </contextlist>
        <usage>
            <p>Defines if the <directive module="core">ServerName</directive> and
               <directive module="core">ServerAlias</directive> values of a VirtualHost
               are automatically added to the members of a Managed Domain or not.
            </p>
        </usage>
    </directivesynopsis>

    <directivesynopsis>
        <name>MDMustStaple</name>
        <description>Control if new certificates carry the OCSP Must Staple flag.</description>
        <syntax>MDMustStaple on|off</syntax>
        <default>MDMustStaple off</default>
        <contextlist>
            <context>server config</context>
        </contextlist>
        <usage>
            <p>Defines if newly requested certificate should have the OCSP Must Staple flag 
            set or not. If a certificate has this flag, the server is required to send a 
            OCSP stapling response to every client. This only works if you configure 
            <module>mod_ssl</module> to generate this (see <directive module="mod_ssl">SSLUseStapling</directive>
            and friends).
            </p>
        </usage>
    </directivesynopsis>

    <directivesynopsis>
        <name>MDNotifyCmd</name>
        <description>Run a program when a Managed Domain is ready.</description>
        <syntax>MDNotifyCmd <var>path</var> [ <var>args</var> ]</syntax>
        <contextlist>
            <context>server config</context>
        </contextlist>
        <usage>
            <p>
                The configured executable is run when a Managed Domain has signed up or
                renewed its certificate. It is given the name of the processed MD as
                additional arguments (after the parameters specified here). It should 
                return status code 0 to indicate that it has run successfully.
            </p>
        </usage>
    </directivesynopsis>

    <directivesynopsis>
        <name>MDPortMap</name>
        <description>Map external to internal ports for domain ownership verification.</description>
        <syntax>MDPortMap <var>map1</var> [ <var>map2</var> ]</syntax>
        <default>MDPortMap http:80 https:443</default>
        <contextlist>
            <context>server config</context>
        </contextlist>
        <usage>
            <p>
                The ACME protocol provides two methods to verify domain ownership via
                HTTP: one that uses 'http:' urls (port 80) and one for 'https:' urls
                (port 443). If your server is not reachable by at least one
                of the two, ACME may only work by configuring your DNS server,
                see <directive module="mod_md">MDChallengeDns01</directive>.
            </p><p>
                On most public facing servers, 'http:' arrives on port 80 and
                'https:' on port 443. The module checks the ports your Apache server
                is listening on and assumes those are available. This means that
                when your server does not listen on port 80, it assumes that
                'http:' requests from the internet will not work.
            </p><p>
                This is a good guess, but it may be wrong. For example, your Apache
                might listen to port 80, but your firewall might block it. 'http:' 
                is only available in your intranet. So, the module will falsely assume
                that Let's Encrypt can use 'http:' challenges with your server. This 
                will then fail, because your firewall will drop those.
            </p>
            <example><title>Example</title>
                <highlight language="config">
MDPortMap http:- https:8433
                </highlight>
            </example>
            <p>
                The above example shows how you can specify that 'http:' requests from 
                the internet will never arrive. In addition it says that 'https:' requests
                will arrive on local port 8433.
            </p><p>
                This is necessary if you have port forwarding in place, your server may be
                reachable from the Internet on port 443, but the local port that httpd uses is
                another one. Your server might only listen on ports 8443 and 8000, but be reached
                on ports 443 and 80 (from the internet).
            </p>
        </usage>
    </directivesynopsis>

    <directivesynopsis>
        <name>MDPrivateKeys</name>
        <description>Set type and size of the private keys generated.</description>
        <syntax>MDPrivateKeys <var>type</var> [ <var>params</var>... ]</syntax>
        <default>MDPrivateKeys RSA 2048</default>
        <contextlist>
            <context>server config</context>
        </contextlist>
        <usage>
            <p>
                Defines what kind of private keys are generated for a managed domain and with
                what parameters. The only supported type right now is 'RSA' and the only parameter
                it takes is the number of bits used for the key.
            </p><p>
                The current (2017) recommendation is at least 2048 bits and a smaller number is
                not accepted here. Higher numbers offer longer security, but are computationally more 
                expensive, e.g. increase the load on your server. That might or might not be an
                issue for you.
            </p><p>
                Other key types will be defined in the future.
            </p>
            <example><title>Example</title>
                <highlight language="config">
MDPrivateKeys RSA 3072
                </highlight>
            </example>
            <p>
                Please note that this setting only has an effect on new keys. Any existing
                private key you have remains unaffected. Also, this only affects private keys
                generated for certificates. ACME account keys are unaffected by this.
            </p>
        </usage>
    </directivesynopsis>

    <directivesynopsis>
        <name>MDRenewWindow</name>
        <description>Control when a certificate will be renewed.</description>
        <syntax>MDRenewWindow <var>duration</var></syntax>
        <default>MDRenewWindow 33%</default>
        <contextlist>
            <context>server config</context>
        </contextlist>
        <usage>
            <p>
            If the validity of the certificate falls below duration, mod_md
            will get a new signed certificate.
            </p><p>
            Normally, certificates are valid for around 90 days and mod_md will renew 
            them the earliest 33% of their complete lifetime before they expire (so for 
            90 days validity, 30 days before it expires). If you think this is not what 
            you need, you can specify either the exact time, as in:
            </p>
            <example><title>Example</title>
                <highlight language="config">
# 21 days before expiry
MDRenewWindow 21d 
# 30 seconds (might be close)
MDRenewWindow 30s
# 10% of the cert lifetime
MDRenewWindow 10%
                </highlight>
            </example>
            <p>When in auto drive mode, the module will check every 12 hours at least 
            what the status of the managed domains is and if it needs to do something. 
            On errors, for example when the CA is unreachable, it will initially retry 
            after some seconds. Should that continue to fail, it will back off to a 
            maximum interval of hourly checks.
            </p>
        </usage>
    </directivesynopsis>

    <directivesynopsis>
        <name>MDRequireHttps</name>
        <description>Redirects http: traffic to https: for Managed Domains.</description>
        <syntax>MDRequireHttps off|temporary|permanent</syntax>
        <default>MDRequireHttps off</default>
        <contextlist>
            <context>server config</context>
        </contextlist>
        <usage>
            <p>This is a convenience directive to ease http: to https: migration of 
            your Managed Domains. With:
            </p>
            <example><title>Example</title>
                <highlight language="config">
MDRequireHttps temporary                
                </highlight>
            </example>
            <p>you announce that you want all traffic via http: URLs to be redirected 
            to the https: ones, for now. This is safe and you can remove this again at
            any time.
            </p><p>
                <strong>The following has consequences: </strong>if you want client to <strong>no longer</strong> use the
             http: URLs, configure:
            </p>
            <example><title>Permanent (for at least half a year!)</title>
                <highlight language="config">
MDRequireHttps permanent                
                </highlight>
            </example>
            <p>This does two things:
            </p>
            <ol>
                <li>All request to the <code>http:</code> resources are redirected to the
                    same url with the <code>https:</code> scheme using the <code>301</code>
                status code. This tells clients that this is intended to be forever and
                the should update any links they have accordingly.
                </li>
                <li>All answers to <code>https:</code> requests will carry the header
                    <code>Strict-Transport-Security</code> with a life time of half a year.
                    This tells the browser that it <strong>never</strong> (for half a year) shall use <code>http:</code>
                    when talking to this domain name. Browsers will, after having seen this, refuse
                    to contact your unencrypted site. This prevents malicious middleware to
                    downgrade connections and listen/manipulate the traffic. Which is good. But
                    you cannot simply take it back again.
                </li>
            </ol>
            <p>You can achieve the same with <module>mod_alias</module> and some
            <directive module="mod_alias">Redirect</directive> configuration,
            basically. If you do it yourself, please make sure to exclude the paths 
            /.well-known/* from your redirection, otherwise mod_md 
            might have trouble signing on new certificates.
            </p>
            <p>If you set this globally, it applies to all managed domains. If you want 
            it for a specific domain only, use:
            </p>
            <example><title>Example</title>
                <highlight language="config">
&lt;MDomain xxx.yyy&gt;
  MDRequireHttps temporary
&lt;/MDomain&gt;
                </highlight>
            </example>
        </usage>
    </directivesynopsis>

    <directivesynopsis>
        <name>MDStoreDir</name>
        <description>Path on the local file system to store the Managed Domains data.</description>
        <syntax>MDStoreDir <var>path</var></syntax>
        <default>MDStoreDir md</default>
        <contextlist>
            <context>server config</context>
        </contextlist>
        <usage>
            <p>
                Defines where on the local file system the Managed Domain data is stored. This is
                an absolute path or interpreted relative to the server root. The default will create
                a directory 'md' in your server root.
            </p><p>
                If you move this and have already data, be sure to move/copy the data first to
                the new location, reconfigure and then restart the server. If you reconfigure
                and restart first, the server will try to get new certificates that it thinks
                are missing.
            </p>
        </usage>
    </directivesynopsis>

    <directivesynopsis>
        <name>MDCAChallenges</name>
        <description>Type of ACME challenge used to prove domain ownership.</description>
        <syntax>MDCAChallenges <var>name</var> [ <var>name</var> ... ]</syntax>
        <default>MDCAChallenges tls-alpn-01 http-01 dns-01</default>
        <contextlist>
            <context>server config</context>
        </contextlist>
        <usage>
            <p>
                Sets challenge types (in order of preference) when proving domain ownership.
                Supported by the module are the challenge methods 'tls-alpn-01', 'dns-01'  
                and 'http-01'. The module will look at the overall configuration of the server 
                to find out which methods can be used. 
            </p><p>
                If the server listens on port 80, for example, the 'http-01' method is available. 
                The prerequisite for 'dns-01' is a configured  <directive module="mod_md">MDChallengeDns01</directive> command. 
                'tls-alpn-01' is described above in 'https: Challenges'.
            </p><p>
                This auto selection works for most setups. But since Apache is a very powerful 
                server with many configuration options, the situation is not clear for all 
                possible cases. For example: it may listen on multiple IP addresses where some 
                are reachable on `https:` and some not.
            </p><p>
                If you configure <directive>MDCAChallenges</directive> directly, this auto selection is disabled. 
                Instead, the module will use the configured challenge list when talking to 
                the ACME server (a challenge type must be offered by the server as well). 
                This challenges are examined in the order specified.
            </p>
        </usage>
    </directivesynopsis>

    <directivesynopsis>
        <name>MDBaseServer</name>
        <description>Control if base server may be managed or only virtual hosts.</description>
        <syntax>MDBaseServer on|off</syntax>
        <default>MDBaseServer off</default>
        <contextlist>
            <context>server config</context>
        </contextlist>
        <usage>
            <p>
            Controls if the base server, the one outside all VirtualHosts should be managed by 
            mod_md or not. By default, it will not. For the very reason that 
            it may have confusing side-effects. It is recommended that you have virtual hosts 
            for all managed domains and do not rely on the global, fallback server configuration.
            </p>
        </usage>
    </directivesynopsis>

    <directivesynopsis>
        <name>MDCertificateFile</name>
        <description>Specify a static certificate file for the MD.</description>
        <syntax>MDCertificateFile <var>path-to-pem-file</var></syntax>
        <contextlist>
            <context>server config</context>
        </contextlist>
        <usage>
            <p>
                This is used inside a <directive module="mod_md">MDomainSet</directive> and specifies
                the file holding the certificate chain for the Managed Domain. The matching
                key is specified via <directive module="mod_md">MDCertificateKeyFile</directive>.
            </p>
            <example><title>Example</title>
                <highlight language="config">
&lt;MDomain mydomain.com>
  MDCertificateFile /etc/ssl/my.cert
  MDCertificateKeyFile /etc/ssl/my.key
&lt;/MDomain>
                </highlight>
            </example>

            <p>
                This is that equivalent of the mod_ssl 
                <directive module="mod_ssl">SSLCertificateFile</directive> directive. It 
                has several uses. 
            </p><p>
                If you want to migrate an existing domain, using static files, to
                automated Let's Encrypt certificates, for one. You define the
                <directive module="mod_md">MDomainSet</directive>, add the files here and remove
                the <directive module="mod_ssl">SSLCertificateFile</directive> from
                your VirtualHosts. 
            </p><p>
                This will give you the same as before, with maybe less repeating lines
                in your configuration. Then you can add <directive module="mod_md">MDRenewMode</directive>
                'always' to it and the module will get a new certificate before
                the one from the file expires. When it has done so, you remove the
                <directive>MDCertificateFile</directive> and reload the server.
            </p><p>
                Another use case is that you renew your Let's Encrypt certificates with
                another ACME clients, for example the excellent 
                <a href="https://certbot.eff.org">certbot</a>. Then let your MDs point
                to the files from certbot and have both working together.
            </p>
        </usage>
    </directivesynopsis>

    <directivesynopsis>
        <name>MDCertificateKeyFile</name>
        <description>Specify a static private key for for the static cerrtificate.</description>
        <syntax>MDCertificateKeyFile <var>path-to-file</var></syntax>
        <contextlist>
            <context>server config</context>
        </contextlist>
        <usage>
            <p>
                This is used inside a <directive module="mod_md">MDomainSet</directive> and specifies
                the file holding the private key for the Managed Domain. The matching
                certificate is specified via <directive module="mod_md">MDCertificateFile</directive>.
            </p><p>
                This is that equivalent of the mod_ssl 
                <directive module="mod_ssl">SSLCertificateKeyFile</directive> directive.
            </p>
        </usage>
    </directivesynopsis>

    <directivesynopsis>
        <name>MDCertificateStatus</name>
        <description>Exposes public certificate information in JSON.</description>
        <syntax>MDCertificateStatus on|off</syntax>
        <default>MDCertificateStatus on</default>
        <contextlist>
            <context>server config</context>
        </contextlist>
        <usage>
            <p>
                When enabled, a resources is available in Managed Domains at
                'https://domain/.httpd/certificate-status' that returns a JSON
                document list key properties of the current and of a renewed
                certificate - when available.
            </p>
            <example><title>Example</title>
                <highlight language="config">
{
  "valid-until": "Thu, 29 Aug 2019 16:06:35 GMT",
  "valid-from": "Fri, 31 May 2019 16:06:35 GMT",
  "serial": "03039C464D454EDE79FCD2CAE859F668F269",
  "sha256-fingerprint": "1ff3bfd2c7c199489ed04df6e29a9b4ea6c015fe8a1b0ce3deb88afc751e352d"
  "renewal" : { ...renewed cert information... }
}                
                </highlight>
            </example>
        </usage>
    </directivesynopsis>


    <directivesynopsis>
        <name>MDChallengeDns01</name>
        <description></description>
        <syntax>MDChallengeDns01 <var>path-to-command</var></syntax>
        <contextlist>
            <context>server config</context>
        </contextlist>
        <usage>
            <p>
                Define a program to be called when the `dns-01` challenge needs to be setup/torn down. 
                The program is given the argument `setup` or `teardown` followed by the domain name. 
                For `setup` the challenge content is additionally given.
            </p><p>
                You do not need to specify this, as long as a 'http:' or 'https:' challenge
                method is possible. However, Let's Encrypt makes 'dns-01' the only
                challenge available for wildcard certificates. If you require
                one of those, you need to configure this.
            </p><p>
                See the section about wildcard certificates above for more details.
            </p>
        </usage>
    </directivesynopsis>

    <directivesynopsis>
        <name>MDMessageCmd</name>
        <description>Handle events for Manage Domains</description>
        <syntax>MDMessageCmd <var>path-to-cmd</var> <var>optional-args</var></syntax>
        <contextlist>
            <context>server config</context>
        </contextlist>
        <usage>
            <p>
                This command gets called when one of the following events happen for
                a Managed Domain: "renewed", "installed", "expiring", "errored". The command may
                be invoked for more than these in the future and ignore events
                it is not prepared to handle.
            </p><p>
                This is the more flexible companion to <directive module="mod_md">MDNotifyCmd</directive>.
            </p>
            <example><title>Example</title>
                <highlight language="config">
MDMessageCmd /etc/apache/md-message
                </highlight>

# will be invoked when a new certificate for mydomain.org is available as:
/etc/apache/md-message renewed mydomain.com
            </example>
            <p>
                The program should not block, as the module will wait for it to finish. A
                return code other than 0 is regarded as an error. 
            </p><p>
                'errored' is no immediate cause for concern since renewal is attempted
                early enough to allow the internet to come back. This is reported at most
                once per hour. 
            </p><p>
                'expiring' should be taken serious. It is issued when the
                <directive module="mod_md">MDWarnWindow</directive> is reached. By default this is
                10% of the certificate lifetime, so for Let's Encrypt this currently
                means 9 days before it expires. The warning is repeated at most once
                a day. 
            </p><p>
                'renewed' means that a new certificate has been obtained and is stored
                in the 'staging' area in the MD store. It will be activated on the next
                server restart/reload.
            </p><p>
                'installed' is triggered when a new certificate has been transferred from
                staging into the domains location in MD store. This happens at server
                startup/reload. Different to all other invocations, <directive>MDMessageCmd</directive> is run
                with root permissions (on *nix systems) and has access to the certificate
                files (and keys). Certificates needed for other applications or
                in different formats can be processed on this event.
            </p>
        </usage>
    </directivesynopsis>

    <directivesynopsis>
        <name>MDWarnWindow</name>
        <description>Define the time window when you want to be warned about an expiring certificate.</description>
        <syntax>MDWarnWindow duration</syntax>
        <default>MDWarnWindow 10%</default>
        <contextlist>
            <context>server config</context>
        </contextlist>
        <usage>
            <p>
                See <directive module="mod_md">MDRenewWindow</directive> for a description on
                how you can specify the time.
            </p><p>
                The modules checks the remaining lifetime of certificates and invokes
                <directive module="mod_md">MDMessageCmd</directive> when there is less than the warn
                window left. With the default, this mean 9 days for certificates from
                Let's Encrypt.
            </p><p>
                It also applies to Managed Domains with static certificate files (
                see <directive module="mod_md">MDCertificateFile</directive>).
            </p>
        </usage>
    </directivesynopsis>

    <directivesynopsis>
        <name>MDServerStatus</name>
        <description>Control if Managed Domain information is added to server-status.</description>
        <syntax>MDServerStatus on|off</syntax>
        <default>MDServerStatus on</default>
        <contextlist>
            <context>server config</context>
        </contextlist>
        <usage>
            <p>
                Apaches 'server-status' handler allows you configure a resource to monitor
                what is going on. This includes now a section listing all Managed Domains
                with the DNS names, renewal status, lifetimes and main properties.
            </p><p>
                You can switch that off using this directive.
            </p>
        </usage>
    </directivesynopsis>

    <directivesynopsis>
        <name>MDCertificateMonitor</name>
        <description>The URL of a certificate log monitor.</description>
        <syntax>MDCertificateMonitor name url</syntax>
        <default>MDCertificateMonitor crt.sh https://crt.sh?q=</default>
        <contextlist>
            <context>server config</context>
        </contextlist>
        <usage>
            <p>
                This is part of the 'server-status' HTML user interface and has nothing to 
                do with the core functioning itself. It defines the link offered on that 
                page for easy checking of a certificate monitor. The SHA256 fingerprint 
                of the certificate is appended to the configured url.
            </p><p>
                Certificate Monitors offer supervision of Certificate Transparency (CT) 
                Logs to track the use of certificates for domains. The least you may see 
                is that Let's Encrypt (or whichever CA you have configured) has entered 
                your certificates into the CTLogs.
            </p><p>
                Caveat: certificate logs update and monitor's intakes of those
                updates suffer some delay. This varies between logs and monitors. A
                brand new certificate will not be known immediately.
            </p>
        </usage>
    </directivesynopsis>

    <directivesynopsis>
        <name>MDStapling</name>
        <description>Enable stapling for all or a particular MDomain.</description>
        <syntax>MDStapling on|off</syntax>
        <default>MDStapling off</default>
        <contextlist>
            <context>server config</context>
        </contextlist>
        <compatibility>Available in version 2.4.42 and later</compatibility>
        <usage>
            <p>
                <module>mod_md</module> offers an implementation for providing OCSP stapling information. 
                This is an alternative to the one provided by <module>mod_ssl</module>. For backward 
                compatibility, this is disabled by default.
            </p><p>
                The stapling can be switched on for all certificates on the server or 
                for an individual <directive module="mod_md">MDomain</directive>.
                This will replace any stapling configuration 
                in <module>mod_ssl</module> for these hosts. When disabled, the <module>mod_ssl</module> stapling 
                will do the work (if it is itself enabled, of course). This allows for
                a gradual shift over from one implementation to the other.
            </p><p>
                The stapling of <module>mod_md</module> will also work for domains where the certificates 
                are not managed by this module (see <directive module="mod_md">MDStapleOthers</directive> for how to control this). 
                This allows use of the new stapling without using any ACME certificate 
                management.
            </p>
        </usage>
    </directivesynopsis>

    <directivesynopsis>
        <name>MDStapleOthers</name>
        <description>Enable stapling for certificates not managed by mod_md.</description>
        <syntax>MDStapleOthers on|off</syntax>
        <default>MDStapleOthers on</default>
        <contextlist>
            <context>server config</context>
        </contextlist>
        <compatibility>Available in version 2.4.42 and later</compatibility>
        <usage>
            <p>
                This setting only takes effect when <directive module="mod_md">MDStapling</directive> is enabled. It controls 
                if <module>mod_md</module> should also provide stapling information for certificates 
                that are not directly controlled by it, e.g. renewed via an ACME CA.
            </p>
        </usage>
    </directivesynopsis>

    <directivesynopsis>
        <name>MDStaplingKeepResponse</name>
        <description>Controls when old responses should be removed.</description>
        <syntax>MDStaplingKeepResponse <var>duration</var></syntax>
        <default>MDStaplingKeepResponse 7d</default>
        <contextlist>
            <context>server config</context>
        </contextlist>
        <compatibility>Available in version 2.4.42 and later</compatibility>
        <usage>
            <p>
                This time window specifies when OCSP response data used in stapling 
                shall be removed from the store again. Response information older than 
                7 days (default) is deleted on server restart/reload. This keeps the store 
                from growing when certificates are renewed/reconfigured frequently.
            </p><p>
            </p>
        </usage>
    </directivesynopsis>

    <directivesynopsis>
        <name>MDStaplingRenewWindow</name>
        <description>Control when the stapling responses will be renewed.</description>
        <syntax>MDStaplingRenewWindow <var>duration</var></syntax>
        <default>MDStaplingRenewWindow 33%</default>
        <contextlist>
            <context>server config</context>
        </contextlist>
        <compatibility>Available in version 2.4.42 and later</compatibility>
        <usage>
            <p>
                If the validity of the OCSP response used in stapling falls below <var>duration</var>, 
                <module>mod_md</module> will obtain a new OCSP response.
            </p><p>
                The CA issuing a certificate commonly also operates the OCSP responder 
                service and determines how long its signed response about the validity 
                of a certificate are itself valid. The longer a response is valid, the longer 
                it can be cached which mean better overall performance for everyone. 
                The shorter the life time, the more rapidly certificate revocations
                spread to clients. Also, service reliability is a consideration.
            </p><p>
                By adjusting the stapling renew window you can control parts of this yourself. 
                If you make the renew time short (e.g. a short time before the current
                information expires), you gain maximum cache time. But a service outage
                (down for maintenance, for example) will affect you. If you renew a long
                time before expiry, updates will be made more frequent, cause more load
                on the CA server infrastructure and also more coordination between
                the child processes of your server.
            </p><p>
                The default is chosen as 33%, which means renewal is started when only 
                a third of the response lifetime is left. For a CA that issues OCSP 
                responses with lifetime of 3 days, this means 2 days of caching and 1 day 
                for renewal attempts. A service outage would have to last full 24 hours 
                to affect your domains.
            </p><p>
                Setting an absolute renew window, like `2d` (2 days), is also possible. 
            </p>
        </usage>
    </directivesynopsis>

    <directivesynopsis>
        <name>MDCertificateCheck</name>
        <description>MDCertificateCheck <var>name</var> <var>url</var></description>
        <syntax></syntax>
        <contextlist>
            <context>server config</context>
        </contextlist>
        <compatibility>Available in version 2.4.42 and later</compatibility>
        <usage>
            <p>
            </p>
        </usage>
    </directivesynopsis>

    <directivesynopsis>
        <name>MDActivationDelay</name>
        <description></description>
        <syntax>MDActivationDelay <var>duration</var><</syntax>
        <contextlist>
        <contextlist>
            <context>server config</context>
        </contextlist>
        <compatibility>Available in version 2.4.42 and later</compatibility>
        <usage>
            <p>
            </p>
        </usage>
    </directivesynopsis>

    <directivesynopsis>
        <name>MDContactEmail</name>
        <description></description>
        <syntax>MDContactEmail <var>address</var></syntax>
        <contextlist>
            <context>server config</context>
        </contextlist>
        <usage>
            <p>
                The ACME protocol requires you to give a contact url when you sign up. Currently, 
                Let's Encrypt wants an email address (and it will use it to inform you about renewals 
                or changed terms of service). <module>mod_md</module> uses the <directive>MDContactEmail</directive> directive email in 
                your Apache configuration, so please specify the correct address there. 
                If <directive>MDContactEmail</directive> is not present, <module>mod_md</module> will use the 
                <directive module="core">ServerAdmin</directive> directive.
            </p>
        </usage>
    </directivesynopsis>
    
</modulesynopsis>