feat(provider): call generateVerificationToken async (#1378)

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 = provider.generateVerificationToken?.() ?? randomBytes(32).toString('hex')
+    const token = await 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)}`

www/docs/providers/email.md

@@ -184,3 +184,17 @@ const text = ({ url, site }) => `Sign in to ${site}\n${url}\n\n`
 :::tip
 If you want to generate great looking email client compatible HTML with React, check out https://mjml.io
 :::
+
+
+## Customising the Verification Token
+
+By default, we are generating a random verification token. You can define a `generateVerificationToken` method in your provider options if you want to override it:
+
+```js title="pages/api/auth/[...nextauth].js"
+providers: [
+  Providers.Email({
+    async generateVerificationToken() {
+      return "ABC123"
+    }
+  })
+],