Ability to get auth providers instances

[idhard]

Would be great to be able to get instances of the auth providers once we set the auth configs.

Something like this

import EmailProvider from "next-auth/providers/email";


/**
 * Options for NextAuth.js used to configure adapters, providers, callbacks, etc.
 *
 * @see https://next-auth.js.org/configuration/options
 */
export const authOptions: NextAuthOptions = {
  callbacks: {}
...
providers: [
  EmailProvider({
     id:"email",
    server: process.env.EMAIL_SERVER,
    from: process.env.EMAIL_FROM
  }),
],



const auth = NextAuth(authOptions);

const provider = auth.providers.get("email");
 
const token = provider.generateVerificationToken()

To be able programatically build the SignIn Url and send it by email from the backend i had to instantiate the providers manually using the core function :

export default function parseProviders(params: {
  providers: Provider[]
  url: URL
  providerId?: string
  options: AuthConfig
}): {
  providers: InternalProvider[]
  provider?: InternalProvider
} {

There are a bunch of issues that will benefit of exposing providers instances to build custom links and tokens

#4208

#45

#5882

thanks