Custom error transformation per flow

NestAuthModule.forRoot({
  // …
  errorHandler(error, context) {
    // context: 'login' | 'signup' | 'password_reset' | 'mfa_verify' | …
 
    if (context === 'login') {
      // Hide whether the email exists
      if (
        error.code === 'EMAIL_NOT_FOUND' ||
        error.code === 'INVALID_CREDENTIALS'
      ) {
        return {
          statusCode: 401,
          errorCode: 'INVALID_CREDENTIALS',
          message: 'Email or password is incorrect',
        };
      }
    }
 
    if (context === 'signup') {
      if (error.code === 'WEAK_PASSWORD') {
        return {
          statusCode: 400,
          errorCode: 'WEAK_PASSWORD',
          message: error.message,
          requirements: {
            minLength: 8,
            mustContainNumber: true,
            mustContainSymbol: true,
          },
        };
      }
    }
 
    // Default: re-throw / pass through
    return null;
  },
});