Support Login Hint for SAML login

[inker-kuo]

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Is your proposal related to a problem?

I checked from the code here that the SAML login don't work with login_hint field:

jackson/npm/src/controller/oauth.ts

Line 492 in 7576341

if (login_hint) {

Can we support it?
My example local setup with NextAuth is

	BoxyHQSAMLProvider({
		authorization: { params: { scope: '' } },
		issuer: "https://xxx.xxx.xxx",
		clientId: "dummy",
		clientSecret: "dummy",
	  }),

Describe the solution you'd like

Can signIn by passing the login_hint in as the following NextAuth example code:

signIn(
  provider.id,
  { callbackUrl: '/' },
  { tenant, product, login_hint: email },
);

And the IdP side can automatically fill it into their login page.

Describe alternatives you've considered

N/A

Additional context

N/A

[niwsa]

@inker-kuo Thanks for creating this issue. Seems like there is no built in support for login_hint under SAML. We might need to look into other options like using relayState for this.