[KEYCLOAK-11499] Add idp-hint as a configuration option

[moremagic]

Add idp-hint as a configuration option, so that gatekeeper can set it's own suggested idp.

[abstractj]

@moremagic I believe this change makes sense, wdyt @stianst?. We need two things here:

1. Tests for the new parameter
2. Update our documentation: https://github.com/keycloak/keycloak-documentation/blob/9194cbe2c4f443ddb4ab012cc9902fc3759bdc6a/securing_apps/topics/oidc/keycloak-gatekeeper.adoc

Please let me know if you would like to proceed, otherwise we may need to schedule the full implementation for the next releases. If you have any questions, feel free to ask.

[msuret]

It would be useful if idp-hint could also be dynamically deduced from the host, e.g. accessing the app from tenant1.myapp.com would set idp_hint to tenant1. What do you think ? I can work on this.

[abstractj]

It would be useful if idp-hint could also be dynamically deduced from the host, e.g. accessing the app from tenant1.myapp.com would set idp_hint to tenant1. What do you think ? I can work on this.

Thanks for volunteering to work on this @msuret. Before start working on anything, I'd suggest starting a thread on the dev mailing list, so others can join and provide some feedback on this.
Also, I didn't have the chance to look at other adapters, but we need to make sure that Gatekeeper has the same behavior as other Keycloak adapters.

[rickyschechter]

Could there sometimes be other url parameters already in authURL? I am thinking "&" vs "?"
If that is never a possibility please disregard, otherwise I suggest adding some pre-inspection of authURL before appending.

[rickyschechter]

Thank you @abstractj and @moremagic ! The change looks simple enough.

Line (91) I added a comment. I agree that tests are missing still.

Could you please point me at where I can download the built artifact? I could probably test it manually and report based on my use/findings.

[abstractj]

@moremagic would you like to follow up on @rickyschechter's comments? Do you have any plans to introduce tests?