Securing an Angular Firebase AI App with Email/Password Authentication (Part 2: Signal Forms Sign-In Modal) [GDE]

In this blog post, we build a Sign-In modal component (SignInModalComponent) using the stable Angular Signal Forms API (@angular/forms/signals) to handle email and password authentication.

Caption: Sign-In Dialog with email and password fields.

Architecture & Mental Model

The sign-in flow works as follows:

• Signal Form Validation: We build a Signal Form with required email and password fields. When validation fails on submit, onInvalid automatically focuses the first invalid control.
• Firebase Authentication: When a user submits valid form fields, SignInModalComponent calls AuthService.signIn() to verify that the submitted email and password match an existing account in Firebase Authentication.
• Route Redirection or Error Handling:
  • Valid credentials: When authentication succeeds (AuthService.isAuthenticated() is true), the modal closes and redirects the user to the /dashboard route, where they can perform AI tasks.
  • Invalid credentials / error thrown: When authentication fails, SignInModalComponent.signIn() updates its errorMessage signal ('Failed to sign in. Please check your credentials and try again.') and returns { kind: 'serverError', message: 'Failed to submit form' }.

flowchart TD
    Submit["User Submits Email & Password"] --> Validate{"signInSchemaValidation()"}
    Validate -- "Invalid" --> Focus["onInvalid: focusBoundControl() on 1st error"]
    Validate -- "Valid" --> Action["submission.action: signIn(field)"]
    Action --> Auth["AuthService.signIn(formValues)"]
    Auth --> Check{"AuthService.isAuthenticated()?"}
    Check -- "true" --> Close["DialogRef.close() + Router.navigate(['/dashboard'])"]
    Check -- "false / throws" --> Error["Set errorMessage signal & return serverError"]

1. Defining the Signal Form Validation Schema

We start by importing the required and email validators from @angular/forms/signals to define signInSchemaValidation(), which returns a SchemaOrSchemaFn<AuthCredentials, PathKind.Root>:

• Required fields (required): The required validator marks both the email and password fields as required with custom error messages ({ message: 'Email is required' } and { message: 'Password is required' }).
• Email format validation (email): The email validator checks that the entered email value is a well-formed email address and returns { message: 'Invalid email format' } when the format is invalid.

// src/app/shared/ui/sign-in-modal/schemas/sign-in.schema.ts
import type { AuthCredentials } from '@/core/auth';
import type { PathKind, SchemaOrSchemaFn } from '@angular/forms/signals';
import { email, required } from '@angular/forms/signals';

export function signInSchemaValidation(): SchemaOrSchemaFn<AuthCredentials, PathKind.Root> {
  return (schemaPath) => {
    required(schemaPath.email, { message: 'Email is required' });
    email(schemaPath.email, { message: 'Invalid email format' });
    required(schemaPath.password, { message: 'Password is required' });
  };
}

2. Building SignInModalComponent with Signal Forms and AuthService

2.1 Injecting Dependencies and Initializing the Signal Form

In SignInModalComponent, we inject the required services and initialize the reactive form model:

• AuthService and Router: Handle Firebase email/password authentication and route navigation after signing in.
• DialogRef: Closes the modal via @angular/cdk/dialog (inject(DialogRef, { optional: true })) when the user clicks the close button or when sign-in succeeds.
• errorMessage: Stores and displays an alert message (signal<string | undefined>(undefined)) when authentication fails.
• signInModel: Backs the Signal Form (signal<AuthCredentials>({ email: '', password: '' })) and initializes the email and password fields to empty strings.

Note

Why @angular/cdk/dialog instead of a native <dialog> element?
If you only need a single modal in an app without @angular/cdk, the native HTML <dialog> element is the better, zero-dependency choice. However, this repository already includes @angular/cdk, and @angular/cdk/dialog provides comprehensive accessibility (a11y) out of the box—including focus trapping, focus restoration, Escape-key dismissal, and ARIA attributes. Because we also dynamically import @angular/cdk/dialog when opening the modal, so it never increases the initial bundle size, it is a practical choice here.

// src/app/core/auth/auth-credentials.interface.ts
export interface AuthCredentials {
  email: string;
  password: string;
}

// src/app/shared/ui/sign-in-modal/sign-in-modal.component.ts (Part 1a: Dependencies & Model)
@Component({
  imports: [FormField, FormRoot, CloseIconComponent, SpinnerIconComponent],
  selector: 'app-sign-in-modal',
})
export class SignInModalComponent {
  readonly #authService = inject(AuthService);
  readonly #dialogRef = inject(DialogRef, { optional: true });
  readonly #router = inject(Router);

  errorMessage = signal<string | undefined>(undefined);

  signInModel = signal<AuthCredentials>({
    email: '',
    password: '',
  });

Next, we pass this.signInModel and signInSchemaValidation() to the form() function to create signInForm. The form() function validates signInModel against the validation schema and configures form submission behavior:

• Valid submission (submission.action): When validation succeeds, form submission executes the action callback, which invokes this.signIn(field).
• Invalid submission (submission.onInvalid): When validation fails, form submission executes the onInvalid callback to locate the first validation error (field().errorSummary()[0]) and automatically focus its bound form control (firstError?.fieldTree().focusBoundControl()).

// src/app/shared/ui/sign-in-modal/sign-in-modal.component.ts (Part 1b: Signal Form)
  signInForm = form(this.signInModel, signInSchemaValidation(), {
    submission: {
      action: async (field) => this.signIn(field),
      onInvalid: (field) => {
        const firstError = field().errorSummary()[0];
        firstError?.fieldTree().focusBoundControl();
      },
    },
  });

2.2 Implementing onClose() and signIn()

Next, let's implement the onClose() and signIn() methods in SignInModalComponent:

• onClose(): Calls this.#dialogRef?.close() when the user clicks the top-right close button to dismiss the modal.
• signIn(): Calls this.#authService.signIn(field().value()) to authenticate the submitted form credentials with Firebase Authentication:
  • Successful authentication: When this.#authService.isAuthenticated() evaluates to true, we close the modal (this.#dialogRef?.close()), navigate to the /dashboard route (await this.#router.navigate([APP_LINKS.DASHBOARD])), and return undefined.
  • Unsuccessful authentication: When authentication fails, we update this.errorMessage.set('Failed to sign in. Please check your credentials and try again.') and return a generic submission error ({ kind: 'serverError', message: 'Failed to submit form' }) so the Signal Form records the failed submission state.

// src/app/shared/ui/sign-in-modal/sign-in-modal.component.ts (Part 2: onClose & signIn)
  onClose(): void {
    this.#dialogRef?.close();
  }

  async signIn(field: FieldTree<AuthCredentials, string | number>): Promise<SignInSubmissionError | undefined> {
    this.errorMessage.set(undefined);
    await this.#authService.signIn(field().value());
    if (this.#authService.isAuthenticated()) {
      this.#dialogRef?.close();
      await this.#router.navigate([APP_LINKS.DASHBOARD]);
      return undefined;
    }
    this.errorMessage.set('Failed to sign in. Please check your credentials and try again.');
    return { kind: 'serverError', message: 'Failed to submit form' };
  }
}

3. Binding the Signal Form in the Template

Now let's wire signInForm to the component template in src/app/shared/ui/sign-in-modal/sign-in-modal.component.html:

• Closing the modal: When a user clicks the top-right close button, onClose() closes the modal via this.#dialogRef?.close().
• Displaying authentication errors: When errorMessage() holds a message (@if (errorMessage(); as msg)), the template renders <div role="alert">{{ msg }}</div> above the form.
• Binding the form root ([formRoot]): The [formRoot] directive binds the <form> element directly to the signInForm form model, connecting form submission to the submission configuration we defined in the component.
• Binding form fields ([formField]): The [formField] directive binds signInForm.email to the email input field and signInForm.password to the password input field.
• Rendering validation errors: When the user interacts with a field (touched()) and it is invalid(), we iterate over its errors() array with @for to output each validation error message ({{ error.message }}).
• Handling the submission state: While the form's async submission.action is running, signInForm().submitting() evaluates to true. We bind [disabled]="signInForm().submitting()" on the submit button to disable it during authentication and prevent concurrent submissions.

<!-- src/app/shared/ui/sign-in-modal/sign-in-modal.component.html (Signal Form excerpt) -->
@if (errorMessage(); as msg) {
  <div role="alert">{{ msg }}</div>
}

<form [formRoot]="signInForm">
  <label for="sign-in-email">
    EMAIL ADDRESS
    <input id="sign-in-email" type="email" autocomplete="username" [formField]="signInForm.email" />
    @if (signInForm.email().touched() && signInForm.email().invalid()) {
      @for (error of signInForm.email().errors(); track error) {
        <span>{{ error.message }}</span>
      }
    }
  </label>

  <label for="sign-in-password">
    PASSWORD
    <input id="sign-in-password" type="password" autocomplete="current-password" [formField]="signInForm.password" />
    @if (signInForm.password().touched() && signInForm.password().invalid()) {
      @for (error of signInForm.password().errors(); track error) {
        <span>{{ error.message }}</span>
      }
    }
  </label>

  <button type="submit" [disabled]="signInForm().submitting()">
    @if (signInForm().submitting()) {
      <app-spinner-icon />
      <span>Signing in...</span>
    } @else {
      <span>Sign In</span>
    }
  </button>
</form>

Caption: Sign-In Dialog with an invalid authentication attempt.

Caption: Sign-In Dialog when the form fields violate the required field validation rules.

Takeaways & What's Next

In Part 2, we built SignInModalComponent and connected it to AuthService:

• Angular Signal Forms Integration: SignInModalComponent uses Angular Signal Forms to define the form model and bind each field to its corresponding HTML <input> element. signInSchemaValidation() validates the form fields. When validation passes, submission.action calls AuthService.signIn() to authenticate the user's credentials; when validation fails, submission.onInvalid automatically focuses the first field with an error.
• Lean Initial Bundles with Dynamic Imports: Even though @angular/cdk is not a lightweight library, we will dynamically import both SignInModalComponent and @angular/cdk/dialog when opening the modal from the Home component. This keeps main.js and our initial bundles lean.

In Part 3, we will build a lightweight Home screen with a Sign In button that opens the CDK Dialog. We will also update the Header component to provide icons for navigating home and logging out. Finally, we will use the AuthService.isAuthenticated() computed signal to conditionally display the Sign In and Launch Studio buttons on the Home screen, and reuse the same signal to show or hide the logout button in the Header component.

Resources

• GitHub Repository: ng-firebase-tts
• Angular Signal Forms
• Angular Signal Form Submission
• Angular CDK Dialog