How do I get the username once logged in with mod_auth_mellon?

Question

I am trying to set up SSO for a php web application. I have configured mod_auth_mellon with apache to redirect to my Idp auth page, and am getting a cookie in response to the login.

My httpd.conf contains the following:

MellonCacheSize 100
MellonLockFile "/var/run/mod_auth_mellon.lock"
MellonPostTTL 900
MellonPostSize 1048576
MellonPostCount 100

<Location /secret>
   Require valid-user
   AuthType "Mellon"
   MellonEnable "auth"
   MellonVariable "cookie"
   MellonSecureCookie On
   MellonCookiePath /
   MellonUser "NAME_ID"
   MellonMergeEnvVars On
   MellonMergeEnvVars On ":"
   MellonEnvVarsIndexStart 1

   MellonSessionDump Off
   MellonSamlResponseDump Off

   MellonEndpointPath "/secret/endpoint"
   MellonDefaultLoginPath "/"

   MellonSessionLength 86400
   MellonNoCookieErrorPage "https://example.com/no_cookie.html"
   MellonSPMetadataFile /etc/apache2/mellon/sp-metadata.xml
   MellonSPPrivateKeyFile /etc/apache2/ssl.key
   MellonSPCertFile /etc/apache2/ssl.crt
   MellonIdPMetadataFile /etc/apache2/mellon/idp-metadata.xml

   MellonSamlResponseDump Off
   MellonSessionDump Off
   MellonAuthnContextClassRef "urn:oasis:names:tc:SAML:2.0:ac:classes:PasswordProtectedTransport"
   MellonECPSendIDPList Off
   MellonRedirectDomains [self]
</Location>

I am getting a result when I have an index.php:

<?php
print_r( $_COOKIE["mellon-cookie"] );
?>

It looks like: 6ce7d6484360f5a98683e0ae87738635

How do I use this to get the username to send to my application?

Edit: I've tried looking at the output of the following:

print_r( $_REQUEST );
print_r( $_SESSION );
print_r( $_POST );
print_r( $_GET );

Answer 1

The data is stored in the $_SERVER variable in php.

The following php prints all keys and values.

<?php
header('Content-Type: text/plain');

foreach($_SERVER as $key=>$value) {
  if(substr($key, 0, 7) == 'MELLON_') {
    echo($key . '=' . $value . "\r\n");
  }
}
?>