Google middleware authorization should use prompt instead of approval_prompt

[hempels]

I see support in GoogleHandler.BuildChallengeUrl for approval_prompt via:
AddQueryString(queryStrings, properties, "approval_prompt");

First, I can't figure out how to apply that property. Setting it in CookieAuthenticationEvents.OnSigningIn doesn't seem to cause any different behavior by Google.

Second, it's not the right property. Google deprecated it in favor of prompt, which has four possible values: "none", "consent", "select_account", or "select_account consent".
see: https://developers.google.com/identity/protocols/OAuth2WebServer

I've managed to work around this limitation by adding ?prompt=select_account to the AuthorizationEndpoint in GoogleOptions, but it's a pretty ugly hack.

[Tratcher]

Those property overrides can be specified in the initial call to Challenge with the AuthenticationProperties collection.

As for approval_prompt, we'll have to dig up the official list of parameters and update it.

[hempels]

One note, I think the current solution is perhaps creating extra work for you guys and for consumers of the API. I struggle to come up with a reason it wouldn't make sense to just provide a parameters dictionary so any value can be passed to the target API. That approach seems to work for WebRequest headers, etc. The way this is implemented now, the library will constantly be chasing API revisions.

In any case, thank you for your attention and for pointing to the proper place to set the parameters.

[Eilon]

We should check the Google docs if approval_prompt is still the right field, and if not, update our codes.

[troydai]

approval_prompt is a legacy parameter. Though it is not in the official document, it is still working. prompt is a different parameter for different usage. We will keep both.

[troydai]

Issue is fixed in ddeef1f

I filed additional issue #990 to track @hempels 's feedback on auth query parameters.