Remove OIDC return_uri hack

[mkosek]

As FreeIPA wiki is running behind proxy, it's internal URI is different from the exposed one. I had to hack OIDC plugin to return a configured return URI, otherwise Ipsilon would reject the OIDC authentication: cc32652.

This hack should be fixed, otherwise the OIDC plugin needs to be hacked again after every update.

[simo5]

Can you upstrem a configuration setting to the plugin, so that everyone benefits from it and we do not have to hack it every time ? Running behind reverse proxies is pretty common these days.

[mkosek]

Related change that works with vendor being built dynamically: 1479e11

[mkosek]

@simo5, yes, that's my plan actually. This is why I created this ticket, to remind me/us to remove this hack!