'issuer' value in .well-known/openid-configuration response is incorrect for a sub-realm

Bug description

The 'issuer' value in the .well-known/openid-configuration output does not match the URL that requested it when a sub-realm is part of the request.

Note that this behaviour in 6.0.0.2 onward is different to the initial 6.0 release and also different to earlier releases due to OPENAM-12784

How to reproduce the issue

1). Install AM 6.0.0.5 and simply create a sub-realm, eg. named IDP and configure for OIDC using the wizard.

2). Request (specifying realm not using DNS alias) using the following format:

http://openam.example.com:8080/AM6/oauth2/IDP/.well-known/openid-configuration

3). Inspect the results and note:

"issuer":"http://openam.example.com:8080/AM6/oauth2/realms/root/realms/IDP"

Expected behaviour (as seen in AM 6.0.0.1 and earlier releases)

Request:

http://openam.example.com:8080/AM6/oauth2/IDP/.well-known/openid-configuration

From the response:

"issuer":"http://openam.example.com:8080/AM6/oauth2/IDP

Current behaviour

Request:

http://openam.example.com:8080/AM6/oauth2/IDP/.well-known/openid-configuration

From the response:

"issuer":"http://openam.example.com:8080/AM6/oauth2/realms/root/realms/IDP"