feat(provider): add option to generate email verification token (#541)

* Add option to generate email verification token

* chore: remove unused import

* refactor: define default generateVerificationToken in-place

* refactor: define default generateVerificationToken in-place

Co-authored-by: Nico Domino <yo@ndo.dev>
Co-authored-by: Balázs Orbán <info@balazsorban.com>

src/server/lib/signin/email.js

@@ -10,7 +10,7 @@ export default async function email (email, provider, options) {
     const secret = provider.secret || options.secret
 
     // Generate token
-    const token = randomBytes(32).toString('hex')
+    const token = provider.generateVerificationToken?.() ?? randomBytes(32).toString('hex')
 
     // Send email with link containing token (the unhashed version)
     const url = `${baseUrl}${basePath}/callback/${encodeURIComponent(provider.id)}?email=${encodeURIComponent(email)}&token=${encodeURIComponent(token)}`