fix(auth): refuse account creation from disposable email domains for every provider

apps/sim/app/oauth-error/page.tsx

@@ -1,5 +1,10 @@
 import type { Metadata } from 'next'
-import { SSO_REQUIRED_ERROR_CODE, SSO_REQUIRED_MESSAGE } from '@/lib/auth/constants'
+import {
+  DISPOSABLE_EMAIL_ERROR_CODE,
+  DISPOSABLE_EMAIL_MESSAGE,
+  SSO_REQUIRED_ERROR_CODE,
+  SSO_REQUIRED_MESSAGE,
+} from '@/lib/auth/constants'
 import { DesktopHandoffShell } from '@/app/desktop/components/desktop-handoff-shell'
 
 export const metadata: Metadata = {
@@ -46,6 +51,12 @@ const FRIENDLY: Record<string, string> = {
    * refused. Retrying the same provider can never succeed — name the way in.
    */
   [SSO_REQUIRED_ERROR_CODE]: SSO_REQUIRED_MESSAGE,
+  /**
+   * Account creation refused for a disposable email domain. Better Auth 1.7 redirects with the
+   * error's code; 1.6 redirects with its message, spaces joined by underscores.
+   */
+  [DISPOSABLE_EMAIL_ERROR_CODE]: DISPOSABLE_EMAIL_MESSAGE,
+  [DISPOSABLE_EMAIL_MESSAGE.split(' ').join('_')]: DISPOSABLE_EMAIL_MESSAGE,
   /** The provider returned no email claim, so there is nothing to sign in as. */
   email_not_found:
     'Your identity provider didn’t share an email address with us, so we couldn’t complete sign-in. Please contact your administrator.',

apps/sim/lib/auth/auth.ts

@@ -45,6 +45,8 @@ import { stableExternalAccountId } from '@/lib/auth/connectors/account-id'
 import { buildConnectorProviders } from '@/lib/auth/connectors/providers'
 import {
   applyRegistrationGate,
+  DISPOSABLE_EMAIL_ERROR_CODE,
+  DISPOSABLE_EMAIL_MESSAGE,
   getRequestedSignInProviderId,
   isSignInProviderAllowed,
 } from '@/lib/auth/constants'
@@ -151,6 +153,7 @@ import {
   processCredentialDraft,
   refuseConflictingCredentialReconnect,
 } from '@/lib/credentials/draft-processor'
+import { isDisposableEmail } from '@/lib/messaging/email/disposable'
 import { sendEmail } from '@/lib/messaging/email/mailer'
 import { getFromEmailAddress, getPersonalEmailFrom } from '@/lib/messaging/email/utils'
 import { quickValidateEmail } from '@/lib/messaging/email/validation'
@@ -361,6 +364,15 @@ export const auth = betterAuth({
           if (isEmailBlockedByAccessControl(user.email, accessControl)) {
             throw new Error('Sign-ups from this email are not allowed.')
           }
+          if (isHosted && (await isDisposableEmail(user.email))) {
+            logger.warn('Refusing account creation for a disposable email domain', {
+              domain: user.email.split('@')[1],
+            })
+            throw new APIError('FORBIDDEN', {
+              code: DISPOSABLE_EMAIL_ERROR_CODE,
+              message: DISPOSABLE_EMAIL_MESSAGE,
+            })
+          }
           return { data: user }
         },
         after: async (user, context) => {

apps/sim/lib/auth/constants.ts

@@ -105,3 +105,12 @@ export const SSO_REQUIRED_ERROR_CODE = 'SSO_REQUIRED'
 
 export const SSO_REQUIRED_MESSAGE =
   'Your organization requires single sign-on. Sign in through your identity provider.'
+
+/**
+ * How an account creation refused for a disposable email domain identifies itself, so the OAuth
+ * error page can name the way forward instead of telling the person to try again.
+ */
+export const DISPOSABLE_EMAIL_ERROR_CODE = 'DISPOSABLE_EMAIL'
+
+export const DISPOSABLE_EMAIL_MESSAGE =
+  'Sign-ups from temporary email addresses aren’t supported. Use an account with a permanent email address.'