State param during logout

[Ayiadim]

Hello, first off I'd like to say how much I appreciate this module and the author(s) for all the effort that has been put into it.

I'd like to request a feature, I could potentially create a PR for it if necessary.

Is your feature request related to a problem? Please describe.
I want to forcibly log out an existing user in order to log them in with an external provider. I want to do this in order to ensure that the user in my application is the same user logged in via the external provider. However, upon logging out the user all context is lost during the round-trip.

Describe the solution you'd like
During logOut, I'd like to be able to pass a state parameter along with the postLogoutRedirectUri and id_token_hint so that after logout I can round-trip state across the redirect.

Additional context
http://docs.identityserver.io/en/3.1.0/endpoints/endsession.html

[jeroenheijmans]

Makes sense to me. 👍

If it's part of the specs then direct support for a state argument might be the way to go. If it's not, but it's supported by major IDSes like IdentityServer, then it might make more sense to implement it a la the customQueryParams?

[vdveer]

For everyone's convenience : https://openid.net/specs/openid-connect-session-1_0.html#RPLogout (yes, it is part of the (oidc session management) spec)

[jeroenheijmans]

Thx @vdveer then it for sure makes sense to add this feature to the library!

I'll tag this with pr-welcome but do note that the release/merge cadence of the project is not super-fast, and up to the maintainer.

[Ayiadim]

PR has been submitted by one of my colleagues: @pmccloghrylaing