Provide a way to set loginHint in Blazor with AAD auth

[juho-hanhimaki]

Some applications provide multiple alternative authentication methods for the user to choose from.

To discover the authentication method automatically the application may ask for user's email address and use it to redirect to correct authentication provider. When the user's email address is already known it should not be asked again by the authentication system.

The Azure AD and MSAL.js library provide the login_hint (AAD) and loginHint (MSAL.js) parameters that can be used to prefill the login email address. At the moment the Microsoft.Authentication.WebAssembly.Msal package doesn't offer any way to set the parameter.

MSAL.js docs
https://azuread.github.io/microsoft-authentication-library-for-js/docs/msal/modules/_authenticationparameters_.html#authenticationparameters

[WarrenCrabb]

Additionally, It would be useful to be able to supply the optional prompt parameter. I have cases where I would like to force a user to re-enter their credentials by using prompt=login.

https://docs.microsoft.com/en-us/azure/active-directory/develop/v2-oauth2-implicit-grant-flow#send-the-sign-in-request

[mkArtakMSFT]

We've moved this issue to the Backlog milestone. This means that it is not going to happen for the coming release. We will reassess the backlog following the current release and consider this item at that time. However, keep in mind that there are many other high priority features with which it will be competing for resources.

[szalapski]

Also need domain hint in addition to login hint. Would you reconsider prioritizing this? It would be a very easy enhancement, just exposing the hint fields that already exist upstream.

As it is now, users get a suboptimal experience of an extra unnecessary "choose your account" prompt when logging in. I can hear it now "Stupid site! I'm already logged in!"

Issue came from https://stackoverflow.com/questions/63605653/is-there-a-way-to-supply-a-domain-hint-for-single-sign-on-using-msal-net-on-a-bl

[szalapski]

"affected-very-few" seems dubious. It affects very few because very few are using Blazor for sites that require auth. This one would be a barrier to increased adoption.