RFC: Support the hosted domain parameter for the Google provider

[Nicolapps]

Google supports a parameter called hd on their authorization URL, which allows the login UI to be restricted to a specific Google Workspace instance. This can be useful when developing internal applications for companies, nonprofits or academic institutions.

It is not possible currently to use this parameter with Lucia. My proposal is to add an optional hostedDomain attribute to Config in packages/oauth/src/providers/google.ts:

  type Config = {
  	clientId: string;
  	clientSecret: string;
  	redirectUri: string;
  	scope?: string[];
  	accessType?: "online" | "offline";
+	hostedDomain?: string;
  };

Other similar librairies such as Passport or The PHP League’s OAuth 2 client have support for this attribute.

I’d love to contribute a pull request to implement this.