feat: block disposable email signups (#2883)

Reject disposable / throwaway email providers (mailinator, yopmail,
10minutemail, ...) across all signup paths: email/password, Google,
Microsoft, personal OIDC and organisation OIDC. Backed by the
mailchecker package (offline, ~55k domains, subdomain-aware).

Exposes a SIGNUP_DISPOSABLE_EMAIL error code so the signup form and
SSO redirect alert can show a dedicated message instead of the
generic 'signup disabled' one.

packages/auth/server/lib/utils/handle-oauth-callback-url.ts

@@ -1,5 +1,9 @@
 import { NEXT_PUBLIC_WEBAPP_URL } from '@documenso/lib/constants/app';
-import { isEmailDomainAllowedForSignup, isSignupEnabledForProvider } from '@documenso/lib/constants/auth';
+import {
+  isDisposableEmail,
+  isEmailDomainAllowedForSignup,
+  isSignupEnabledForProvider,
+} from '@documenso/lib/constants/auth';
 import { AppError, AppErrorCode } from '@documenso/lib/errors/app-error';
 import { onCreateUserHook } from '@documenso/lib/server-only/user/create-user';
 import { deletedServiceAccountEmail } from '@documenso/lib/server-only/user/service-accounts/deleted-account';
@@ -132,6 +136,15 @@ export const handleOAuthCallbackUrl = async (options: HandleOAuthCallbackUrlOpti
     return c.redirect(errorUrl.toString(), 302);
   }
 
+  // Reject disposable / throwaway email providers for new SSO users.
+  if (isDisposableEmail(email)) {
+    const errorUrl = new URL('/signin', NEXT_PUBLIC_WEBAPP_URL());
+
+    errorUrl.searchParams.set('error', AuthenticationErrorCode.SignupDisposableEmail);
+
+    return c.redirect(errorUrl.toString(), 302);
+  }
+
   // Handle new user.
   const createdUser = await prisma.$transaction(async (tx) => {
     const user = await tx.user.create({

packages/auth/server/lib/utils/handle-oauth-organisation-callback-url.ts

@@ -1,5 +1,5 @@
 import { sendOrganisationAccountLinkConfirmationEmail } from '@documenso/ee/server-only/lib/send-organisation-account-link-confirmation-email';
-import { isSignupEnabledForProvider } from '@documenso/lib/constants/auth';
+import { isDisposableEmail, isSignupEnabledForProvider } from '@documenso/lib/constants/auth';
 import { AppError } from '@documenso/lib/errors/app-error';
 import { onCreateUserHook } from '@documenso/lib/server-only/user/create-user';
 import { formatOrganisationLoginUrl } from '@documenso/lib/utils/organisation-authentication-portal';
@@ -74,6 +74,15 @@ export const handleOAuthOrganisationCallbackUrl = async (options: HandleOAuthOrg
       return c.redirect(errorUrl.toString(), 302);
     }
 
+    // Reject disposable / throwaway email providers for new SSO users.
+    if (isDisposableEmail(email)) {
+      const errorUrl = new URL(formatOrganisationLoginUrl(orgUrl));
+
+      errorUrl.searchParams.set('error', AuthenticationErrorCode.SignupDisposableEmail);
+
+      return c.redirect(errorUrl.toString(), 302);
+    }
+
     userToLink = await prisma.user.create({
       data: {
         email: email,