Puppet Server: External SSL Termination

Included in Puppet Enterprise 3.7. A newer version is available; see the version menu above for details.

In network configurations that require external SSL termination, there are some important differences between configuring the Apache/Passenger stack and configuring Puppet Server. Use the following steps to configure external SSL termination.

Disable HTTPS for Puppet Server

You’ll need to turn off SSL and have Puppet Server use the HTTP protocol instead: remove the ssl-port and ssl-host settings from the conf.d/webserver.conf file and replace them with port and host settings. See Configuring the Webserver Service for more information on configuring the web server service.

Allow Client Cert Data From HTTP Headers

When using external SSL termination, Puppet Server expects to receive client certificate information via some HTTP headers.

By default, reading this data from headers is disabled. To allow Puppet Server to recognize it, edit (or create) config.d/master.conf and add allow-header-cert-info: true to the master config section. See Puppet Server Configuration for more information on the master.conf file.

WARNING: Setting allow-header-cert-info to ‘true’ puts Puppet Server in an incredibly vulnerable state. Take extra caution to ensure it is absolutely not reachable by an untrusted network.

With allow-header-cert-info set to ‘true’, core Ruby Puppet application code will use only the client HTTP header values—not an SSL-layer client certificate—to determine the client subject name, authentication status, and trusted facts. This is true even if the web server is hosting an HTTPS connection. This applies to validation of the client via rules in the auth.conf file and any trusted facts extracted from certificate extensions.

If the client-auth setting in the webserver config block is set to need or want, the Jetty web server will still validate the client certificate against a certificate authority store, but it will only verify the SSL-layer client certificate—not a certificate in an X-Client-Cert header.

Restart Puppet Server

You’ll need to restart Puppet Server for the configuration changes to take effect.

Configure SSL Terminating Proxy to Set HTTP Headers

The device that terminates SSL for Puppet Server must extract information from the client’s certificate and insert that information into three HTTP headers. See the documentation for your SSL terminator for details.

The headers you’ll need to set are X-Client-Verify, X-Client-DN, and X-Client-Cert.

X-Client-Verify

Mandatory. Must be either SUCCESS if the certificate was validated, or something else if not. (The convention seems to be to use NONE for when a certificate wasn’t presented, and FAILED:reason for other validation failures.) Puppet Server uses this to authorize requests; only requests with a value of SUCCESS will be considered authenticated.

You can change this header name with the ssl_client_verify_header setting.

This setting (and its twin, ssl_client_header) is a bit odd: its value should be the result of transforming the desired HTTP header name into a CGI-style environment variable name. That is, to change the HTTP header to X-SSL-Client-Verify, you would set the setting to HTTP_X_SSL_CLIENT_VERIFY. (Add HTTP_ to the front, change hyphens to underscores, and uppercase everything.)

(Puppet Server will eventually UN-munge the CGI variable name to get a valid HTTP header name, and use that name to interact directly with an HTTP request. This is a legacy quirk to ensure that the setting works the same for both Puppet Server and a Rack Puppet master; note that Rack actually does use CGI environment variables.)

X-Client-DN

Mandatory. Must be the Subject DN of the agent’s certificate, if a certificate was presented. Puppet Server uses this to authorize requests.

Note: Currently, the DN must be in RFC-2253 format (comma-delimited). Due to a bug (SERVER-213), Puppet Server can’t decode OpenSSL-style DNs (slash-delimited). Note that Apache’s mod_ssl SSL_CLIENT_S_DN variable uses OpenSSL-style DNs.

You can change this header name with the ssl_client_header setting. See the note above for more info about this setting’s expected values.

X-Client-Cert

Optional. Should contain the client’s PEM-formatted (Base-64) certificate (if a certificate was presented) in a single URI-encoded string. Note that URL encoding is not sufficient; all space characters must be encoded as %20 and not + characters.

Note: Puppet Server only uses the value of this header to extract trusted facts from extensions in the client certificate. If you aren’t using trusted facts, you can choose to reduce the size of the request payload by omitting the X-Client-Cert header.

Note: Apache’s mod_proxy converts line breaks in PEM documents to spaces for some reason, and Puppet Server can’t decode the result. We’re tracking this issue as SERVER-217.

The name of this header is not configurable.

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