feat(auth): implement view data persistence in 2FA flows

Add persistence to two-factor authentication in the extension login flow. Implements caching of form state to improve user experience when navigating between authentication steps. Includes feature flag for controlled rollout.

libs/auth/src/angular/two-factor-auth/two-factor-auth-component-cache.service.ts

@@ -0,0 +1,105 @@
+import { inject, Injectable, WritableSignal } from "@angular/core";
+import { Jsonify } from "type-fest";
+
+import { ViewCacheService } from "@bitwarden/angular/platform/abstractions/view-cache.service";
+import { TwoFactorProviderType } from "@bitwarden/common/auth/enums/two-factor-provider-type";
+import { FeatureFlag } from "@bitwarden/common/enums/feature-flag.enum";
+import { ConfigService } from "@bitwarden/common/platform/abstractions/config/config.service";
+
+const TWO_FACTOR_AUTH_COMPONENT_CACHE_KEY = "two-factor-auth-component-cache";
+
+/**
+ * Cache model for the two factor authentication data.
+ */
+export class TwoFactorAuthComponentCache {
+  token: string | undefined = undefined;
+  remember: boolean | undefined = undefined;
+  selectedProviderType: TwoFactorProviderType | undefined = undefined;
+
+  static fromJSON(
+    obj: Partial<Jsonify<TwoFactorAuthComponentCache>>,
+  ): TwoFactorAuthComponentCache | null {
+    // Return null if the cache is empty
+    if (obj == null) {
+      return null;
+    }
+
+    return Object.assign(new TwoFactorAuthComponentCache(), obj);
+  }
+}
+
+export interface TwoFactorAuthComponentData {
+  token?: string;
+  remember?: boolean;
+  selectedProviderType?: TwoFactorProviderType;
+}
+
+/**
+ * Cache service used for the two factor auth component.
+ */
+@Injectable()
+export class TwoFactorAuthComponentCacheService {
+  private viewCacheService: ViewCacheService = inject(ViewCacheService);
+  private configService: ConfigService = inject(ConfigService);
+
+  /** True when the `PM9115_TwoFactorExtensionDataPersistence` flag is enabled */
+  private featureEnabled: boolean = false;
+
+  /**
+   * Signal for the cached TwoFactorAuthData.
+   */
+  private twoFactorAuthComponentCache: WritableSignal<TwoFactorAuthComponentCache | null> =
+    this.viewCacheService.signal<TwoFactorAuthComponentCache | null>({
+      key: TWO_FACTOR_AUTH_COMPONENT_CACHE_KEY,
+      initialValue: null,
+      deserializer: TwoFactorAuthComponentCache.fromJSON,
+    });
+
+  constructor() {}
+
+  /**
+   * Must be called once before interacting with the cached data.
+   */
+  async init() {
+    this.featureEnabled = await this.configService.getFeatureFlag(
+      FeatureFlag.PM9115_TwoFactorExtensionDataPersistence,
+    );
+  }
+
+  /**
+   * Update the cache with the new TwoFactorAuthData.
+   */
+  cacheData(data: TwoFactorAuthComponentData): void {
+    if (!this.featureEnabled) {
+      return;
+    }
+
+    this.twoFactorAuthComponentCache.set({
+      token: data.token,
+      remember: data.remember,
+      selectedProviderType: data.selectedProviderType,
+    } as TwoFactorAuthComponentCache);
+  }
+
+  /**
+   * Clears the cached TwoFactorAuthData.
+   */
+  clearCachedData(): void {
+    if (!this.featureEnabled) {
+      return;
+    }
+
+    this.twoFactorAuthComponentCache.set(null);
+  }
+
+  /**
+   * Returns the cached TwoFactorAuthData (when available).
+   */
+  getCachedData(): TwoFactorAuthComponentCache | null {
+    if (!this.featureEnabled) {
+      return null;
+    }
+
+    return this.twoFactorAuthComponentCache();
+  }
+}