Shibboleth does pass attribute to server variable in PHP

I am building a SAML based federated authentication mechanism in which the IdP is ADFS 2.0 and the SP is Shibboleth running on Linux. I am able to do the following:

1. Attempt to access a protected page, which redirects me to the IdP login page.


2. Log in via the IdP login page and get returned to the protected page.


3. Browse to spserver.internal/Shibboleth.sso/Session and see the returned attributes, including eppn.

I am, however, unable to extract the eppn attribute in the form of the REMOTE_USER header in PHP.

I have disabled attribute-policy.xml (commented it out in shibboleth2.xml).

I am missing something trivial, I suspect for the world of me I don't know what. Either PHP is not picking up the server variables set by Shibboleth or Shibboleth is never setting them. Any ideas?

Output from spserver.internal/Shibboleth.sso/Session

Miscellaneous
Session Expiration (barring inactivity): 479 minute(s)
Client Address: a.b.c.d
SSO Protocol: urn:oasis:names:tc:SAML:2.0:protocol
Identity Provider: http://veragence.thesixthflag.com/adfs/services/trust
Authentication Time: 2014-10-28T11:55:23.947Z

Authentication Context Class: urn:oasis:names:tc:SAML:2.0:ac:classes:PasswordProtectedTransport
Authentication Context Decl: (none)

Attributes
eppn: user.id@adfs.idp.server

Relevant line from shibboleth2.xml:

    
                     REMOTE_USER="eppn persistent-id targeted-id">

Relevant line from attribute-map.xml

Relevant output from shibd.log

2014-10-28 11:55:21 DEBUG Shibboleth.SSO.SAML2 [2]: extracting issuer from SAML 2.0 assertion
2014-10-28 11:55:21 DEBUG OpenSAML.SecurityPolicyRule.MessageFlow [2]: evaluating message flow policy (replay checking on, expiration 60)
2014-10-28 11:55:21 DEBUG XMLTooling.StorageService [2]: inserted record (_06157709-48ab-4701-90b2-b3ecea5df51f) in context (MessageFlow) with expiration (1414497564)
2014-10-28 11:55:21 DEBUG OpenSAML.SecurityPolicyRule.XMLSigning [2]: validating signature profile
2014-10-28 11:55:21 DEBUG XMLTooling.TrustEngine.ExplicitKey [2]: attempting to validate signature with the peer's credentials
2014-10-28 11:55:21 DEBUG XMLTooling.TrustEngine.ExplicitKey [2]: signature validated with credential
2014-10-28 11:55:21 DEBUG OpenSAML.SecurityPolicyRule.XMLSigning [2]: signature verified against message issuer
2014-10-28 11:55:21 DEBUG OpenSAML.SecurityPolicyRule.BearerConfirmation [2]: assertion satisfied bearer confirmation requirements

2014-10-28 11:55:21 DEBUG Shibboleth.SSO.SAML2 [2]: SSO profile processing completed successfully
2014-10-28 11:55:21 DEBUG Shibboleth.SSO.SAML2 [2]: extracting pushed attributes...
2014-10-28 11:55:21 DEBUG Shibboleth.AttributeExtractor.XML [2]: unable to extract attributes, unknown XML object type: samlp:Response
2014-10-28 11:55:21 DEBUG Shibboleth.AttributeExtractor.XML [2]: unable to extract attributes, unknown XML object type: {urn:oasis:names:tc:SAML:2.0:assertion}AuthnStatement
2014-10-28 11:55:21 INFO Shibboleth.AttributeExtractor.XML [2]: skipping unmapped SAML 2.0 Attribute with Name: http://schemas.xmlsoap.org/ws/2005/05/identity/claims/upn, Format:urn:oasis:names:tc:SAML:2.0:attrname-format:unspecified
2014-10-28 11:55:21 DEBUG Shibboleth.AttributeDecoder.Scoped [2]: decoding ScopedAttribute (eppn) from SAML 2 Attribute (urn:oid:1.3.6.1.4.1.5923.1.1.1.6) with 1 value(s)
2014-10-28 11:55:21 DEBUG Shibboleth.SSO.SAML2 [2]: resolving attributes...
2014-10-28 11:55:21 DEBUG Shibboleth.AttributeResolver.Query [2]: found AttributeStatement in input to new session, skipping query
2014-10-28 11:55:21 DEBUG Shibboleth.SessionCache [2]: creating new session
2014-10-28 11:55:21 DEBUG Shibboleth.SessionCache [2]: storing new session..