[gateway] support POST method for the end_session_endpoint

[tcompiegne]

User story

As a certified OpenID Connect platform, OpenID Providers MUST support the use of the HTTP GET and POST methods at the Logout Endpoint. RPs MAY use the HTTP GET or POST methods to send the logout request to the OP. If using the HTTP GET method, the request parameters are serialized using URI Query String Serialization. If using the HTTP POST method, the request parameters are serialized using Form Serialization.

https://openid.net/specs/openid-connect-rpinitiated-1_0.html#RPLogout

Possible solution

Add a lastLogout date to the user profile. Check this date against the lastLogin date in the SSOSessionHandler.
This endpoint with POST method must require the use of the id_token_hint as a parameter (Browser cookies are not accessible at this stage).

How to test

• Create a security domain
• Create a user
• Create a web application
• Assign an identity provider
• Sign-in to your account
• Call the LogoutEndpoint with a POST method
• Try to get an access token again (/oauth/authorize)
• User should be asked to sign in to its account