diff --git a/libs/common/spec/observable-tracker.ts b/libs/common/spec/observable-tracker.ts
index 0ec4aa812f8..adefabb7472 100644
--- a/libs/common/spec/observable-tracker.ts
+++ b/libs/common/spec/observable-tracker.ts
@@ -1,13 +1,33 @@
 // FIXME: Update this file to be type safe and remove this and next line
 // @ts-strict-ignore
-import { firstValueFrom, Observable, Subject, Subscription, throwError, timeout } from "rxjs";
+import {
+  filter,
+  firstValueFrom,
+  lastValueFrom,
+  Observable,
+  Subject,
+  Subscription,
+  throwError,
+  timeout,
+} from "rxjs";
 
 /** Test class to enable async awaiting of observable emissions */
 export class ObservableTracker<T> {
   private subscription: Subscription;
   private emissionReceived = new Subject<T>();
   emissions: T[] = [];
-  constructor(observable: Observable<T>) {
+
+  /**
+   * Creates a new ObservableTracker and instantly subscribes to the given observable.
+   * @param observable The observable to track
+   * @param clone Whether to clone tracked emissions or not, defaults to true.
+   *              Cloning can be necessary if the observable emits objects that are mutated after emission. Cloning makes it
+   *              harder to compare the original and the tracked emission using reference equality (e.g. `expect().toBe()`).
+   */
+  constructor(
+    observable: Observable<T>,
+    private clone = true,
+  ) {
     this.emissions = this.trackEmissions(observable);
   }
 
@@ -33,6 +53,19 @@ export class ObservableTracker<T> {
     );
   }
 
+  async expectCompletion(msTimeout = 50): Promise<void> {
+    return await lastValueFrom(
+      this.emissionReceived.pipe(
+        filter(() => false),
+        timeout({
+          first: msTimeout,
+          with: () => throwError(() => new Error("Timeout exceeded waiting for completion.")),
+        }),
+      ),
+      { defaultValue: undefined },
+    );
+  }
+
   /** Awaits until the total number of emissions observed by this tracker equals or exceeds {@link count}
    * @param count The number of emissions to wait for
    */
@@ -48,26 +81,31 @@ export class ObservableTracker<T> {
     this.emissionReceived.subscribe((value) => {
       emissions.push(value);
     });
-    this.subscription = observable.subscribe((value) => {
-      if (value == null) {
-        this.emissionReceived.next(null);
-        return;
-      }
-
-      switch (typeof value) {
-        case "string":
-        case "number":
-        case "boolean":
-          this.emissionReceived.next(value);
-          break;
-        case "symbol":
-          // Cheating types to make symbols work at all
-          this.emissionReceived.next(value as T);
-          break;
-        default: {
-          this.emissionReceived.next(clone(value));
+    this.subscription = observable.subscribe({
+      next: (value) => {
+        if (value == null) {
+          this.emissionReceived.next(null);
+          return;
         }
-      }
+
+        switch (typeof value) {
+          case "string":
+          case "number":
+          case "boolean":
+            this.emissionReceived.next(value);
+            break;
+          case "symbol":
+            // Cheating types to make symbols work at all
+            this.emissionReceived.next(value as T);
+            break;
+          default: {
+            this.emissionReceived.next(this.clone ? clone(value) : value);
+          }
+        }
+      },
+      complete: () => {
+        this.emissionReceived.complete();
+      },
     });
 
     return emissions;
diff --git a/libs/common/src/platform/abstractions/sdk/sdk.service.ts b/libs/common/src/platform/abstractions/sdk/sdk.service.ts
index 22ad2b44ff9..3adf3291bbf 100644
--- a/libs/common/src/platform/abstractions/sdk/sdk.service.ts
+++ b/libs/common/src/platform/abstractions/sdk/sdk.service.ts
@@ -5,6 +5,12 @@ import { BitwardenClient } from "@bitwarden/sdk-internal";
 import { UserId } from "../../../types/guid";
 import { Rc } from "../../misc/reference-counting/rc";
 
+export class UserNotLoggedInError extends Error {
+  constructor(userId: UserId) {
+    super(`User (${userId}) is not logged in`);
+  }
+}
+
 export abstract class SdkService {
   /**
    * Retrieve the version of the SDK.
@@ -26,7 +32,20 @@ export abstract class SdkService {
    * The client will be destroyed when the observable is no longer subscribed to.
    * Please let platform know if you need a client that is not destroyed when the observable is no longer subscribed to.
    *
-   * @param userId
+   * @param userId The user id for which to retrieve the client
+   *
+   * @throws {UserNotLoggedInError} If the user is not logged in
    */
   abstract userClient$(userId: UserId): Observable<Rc<BitwardenClient> | undefined>;
+
+  /**
+   * This method is used during/after an authentication procedure to set a new client for a specific user.
+   * It can also be used to unset the client when a user logs out, this will result in:
+   *  - The client being disposed of
+   *  - All subscriptions to the client being completed
+   *  - Any new subscribers receiving an error
+   * @param userId The user id for which to set the client
+   * @param client The client to set for the user. If undefined, the client will be unset.
+   */
+  abstract setClient(userId: UserId, client: BitwardenClient | undefined): void;
 }
diff --git a/libs/common/src/platform/services/sdk/default-sdk.service.spec.ts b/libs/common/src/platform/services/sdk/default-sdk.service.spec.ts
index e8dfde863ec..fed4746acd3 100644
--- a/libs/common/src/platform/services/sdk/default-sdk.service.spec.ts
+++ b/libs/common/src/platform/services/sdk/default-sdk.service.spec.ts
@@ -4,12 +4,14 @@ import { BehaviorSubject, firstValueFrom, of } from "rxjs";
 import { KdfConfigService, KeyService, PBKDF2KdfConfig } from "@bitwarden/key-management";
 import { BitwardenClient } from "@bitwarden/sdk-internal";
 
+import { ObservableTracker } from "../../../../spec";
 import { AccountInfo, AccountService } from "../../../auth/abstractions/account.service";
 import { UserId } from "../../../types/guid";
 import { UserKey } from "../../../types/key";
 import { Environment, EnvironmentService } from "../../abstractions/environment.service";
 import { PlatformUtilsService } from "../../abstractions/platform-utils.service";
 import { SdkClientFactory } from "../../abstractions/sdk/sdk-client-factory";
+import { UserNotLoggedInError } from "../../abstractions/sdk/sdk.service";
 import { Rc } from "../../misc/reference-counting/rc";
 import { EncryptedString } from "../../models/domain/enc-string";
 import { SymmetricCryptoKey } from "../../models/domain/symmetric-crypto-key";
@@ -26,8 +28,6 @@ describe("DefaultSdkService", () => {
     let keyService!: MockProxy<KeyService>;
     let service!: DefaultSdkService;
 
-    let mockClient!: MockProxy<BitwardenClient>;
-
     beforeEach(() => {
       sdkClientFactory = mock<SdkClientFactory>();
       environmentService = mock<EnvironmentService>();
@@ -47,15 +47,10 @@ describe("DefaultSdkService", () => {
         kdfConfigService,
         keyService,
       );
-
-      mockClient = mock<BitwardenClient>();
-      mockClient.crypto.mockReturnValue(mock());
-      sdkClientFactory.createSdkClient.mockResolvedValue(mockClient);
     });
 
     describe("given the user is logged in", () => {
       const userId = "user-id" as UserId;
-
       beforeEach(() => {
         environmentService.getEnvironment$
           .calledWith(userId)
@@ -75,56 +70,144 @@ describe("DefaultSdkService", () => {
         keyService.encryptedOrgKeys$.calledWith(userId).mockReturnValue(of({}));
       });
 
-      it("creates an SDK client when called the first time", async () => {
-        await firstValueFrom(service.userClient$(userId));
+      describe("given no client override has been set for the user", () => {
+        let mockClient!: MockProxy<BitwardenClient>;
 
-        expect(sdkClientFactory.createSdkClient).toHaveBeenCalled();
+        beforeEach(() => {
+          mockClient = createMockClient();
+          sdkClientFactory.createSdkClient.mockResolvedValue(mockClient);
+        });
+
+        it("creates an internal SDK client when called the first time", async () => {
+          await firstValueFrom(service.userClient$(userId));
+
+          expect(sdkClientFactory.createSdkClient).toHaveBeenCalled();
+        });
+
+        it("does not create an SDK client when called the second time with same userId", async () => {
+          const subject_1 = new BehaviorSubject<Rc<BitwardenClient> | undefined>(undefined);
+          const subject_2 = new BehaviorSubject<Rc<BitwardenClient> | undefined>(undefined);
+
+          // Use subjects to ensure the subscription is kept alive
+          service.userClient$(userId).subscribe(subject_1);
+          service.userClient$(userId).subscribe(subject_2);
+
+          // Wait for the next tick to ensure all async operations are done
+          await new Promise(process.nextTick);
+
+          expect(subject_1.value.take().value).toBe(mockClient);
+          expect(subject_2.value.take().value).toBe(mockClient);
+          expect(sdkClientFactory.createSdkClient).toHaveBeenCalledTimes(1);
+        });
+
+        it("destroys the internal SDK client when all subscriptions are closed", async () => {
+          const subject_1 = new BehaviorSubject<Rc<BitwardenClient> | undefined>(undefined);
+          const subject_2 = new BehaviorSubject<Rc<BitwardenClient> | undefined>(undefined);
+          const subscription_1 = service.userClient$(userId).subscribe(subject_1);
+          const subscription_2 = service.userClient$(userId).subscribe(subject_2);
+          await new Promise(process.nextTick);
+
+          subscription_1.unsubscribe();
+          subscription_2.unsubscribe();
+
+          await new Promise(process.nextTick);
+          expect(mockClient.free).toHaveBeenCalledTimes(1);
+        });
+
+        it("destroys the internal SDK client when the userKey is unset (i.e. lock or logout)", async () => {
+          const userKey$ = new BehaviorSubject(
+            new SymmetricCryptoKey(new Uint8Array(64)) as UserKey,
+          );
+          keyService.userKey$.calledWith(userId).mockReturnValue(userKey$);
+
+          const subject = new BehaviorSubject<Rc<BitwardenClient> | undefined>(undefined);
+          service.userClient$(userId).subscribe(subject);
+          await new Promise(process.nextTick);
+
+          userKey$.next(undefined);
+          await new Promise(process.nextTick);
+
+          expect(mockClient.free).toHaveBeenCalledTimes(1);
+          expect(subject.value).toBe(undefined);
+        });
       });
 
-      it("does not create an SDK client when called the second time with same userId", async () => {
-        const subject_1 = new BehaviorSubject<Rc<BitwardenClient> | undefined>(undefined);
-        const subject_2 = new BehaviorSubject<Rc<BitwardenClient> | undefined>(undefined);
+      describe("given overrides are used", () => {
+        it("does not create a new client and emits the override client when a client override has already been set ", async () => {
+          const mockClient = mock<BitwardenClient>();
+          service.setClient(userId, mockClient);
+          const userClientTracker = new ObservableTracker(service.userClient$(userId), false);
+          await userClientTracker.pauseUntilReceived(1);
 
-        // Use subjects to ensure the subscription is kept alive
-        service.userClient$(userId).subscribe(subject_1);
-        service.userClient$(userId).subscribe(subject_2);
+          expect(sdkClientFactory.createSdkClient).not.toHaveBeenCalled();
+          expect(userClientTracker.emissions[0].take().value).toBe(mockClient);
+        });
 
-        // Wait for the next tick to ensure all async operations are done
-        await new Promise(process.nextTick);
+        it("emits the internal client then switches to override when an override is set", async () => {
+          const mockInternalClient = createMockClient();
+          const mockOverrideClient = createMockClient();
+          sdkClientFactory.createSdkClient.mockResolvedValue(mockInternalClient);
+          const userClientTracker = new ObservableTracker(service.userClient$(userId), false);
 
-        expect(subject_1.value.take().value).toBe(mockClient);
-        expect(subject_2.value.take().value).toBe(mockClient);
-        expect(sdkClientFactory.createSdkClient).toHaveBeenCalledTimes(1);
-      });
+          await userClientTracker.pauseUntilReceived(1);
+          expect(userClientTracker.emissions[0].take().value).toBe(mockInternalClient);
 
-      it("destroys the SDK client when all subscriptions are closed", async () => {
-        const subject_1 = new BehaviorSubject<Rc<BitwardenClient> | undefined>(undefined);
-        const subject_2 = new BehaviorSubject<Rc<BitwardenClient> | undefined>(undefined);
-        const subscription_1 = service.userClient$(userId).subscribe(subject_1);
-        const subscription_2 = service.userClient$(userId).subscribe(subject_2);
-        await new Promise(process.nextTick);
+          service.setClient(userId, mockOverrideClient);
 
-        subscription_1.unsubscribe();
-        subscription_2.unsubscribe();
+          await userClientTracker.pauseUntilReceived(2);
+          expect(userClientTracker.emissions[1].take().value).toBe(mockOverrideClient);
+        });
 
-        await new Promise(process.nextTick);
-        expect(mockClient.free).toHaveBeenCalledTimes(1);
-      });
+        it("throws error when the client has explicitly been set as undefined", async () => {
+          service.setClient(userId, undefined);
 
-      it("destroys the SDK client when the userKey is unset (i.e. lock or logout)", async () => {
-        const userKey$ = new BehaviorSubject(new SymmetricCryptoKey(new Uint8Array(64)) as UserKey);
-        keyService.userKey$.calledWith(userId).mockReturnValue(userKey$);
+          const result = () => firstValueFrom(service.userClient$(userId));
 
-        const subject = new BehaviorSubject<Rc<BitwardenClient> | undefined>(undefined);
-        service.userClient$(userId).subscribe(subject);
-        await new Promise(process.nextTick);
+          await expect(result).rejects.toThrow(UserNotLoggedInError);
+        });
 
-        userKey$.next(undefined);
-        await new Promise(process.nextTick);
+        it("completes the subscription when the override is set to undefined after having been defined", async () => {
+          const mockOverrideClient = createMockClient();
+          service.setClient(userId, mockOverrideClient);
+          const userClientTracker = new ObservableTracker(service.userClient$(userId), false);
+          await userClientTracker.pauseUntilReceived(1);
 
-        expect(mockClient.free).toHaveBeenCalledTimes(1);
-        expect(subject.value).toBe(undefined);
+          service.setClient(userId, undefined);
+
+          await userClientTracker.expectCompletion();
+        });
+
+        it("destroys the internal client when an override is set", async () => {
+          const mockInternalClient = createMockClient();
+          const mockOverrideClient = createMockClient();
+          sdkClientFactory.createSdkClient.mockResolvedValue(mockInternalClient);
+          const userClientTracker = new ObservableTracker(service.userClient$(userId), false);
+
+          await userClientTracker.pauseUntilReceived(1);
+          service.setClient(userId, mockOverrideClient);
+          await userClientTracker.pauseUntilReceived(2);
+
+          expect(mockInternalClient.free).toHaveBeenCalled();
+        });
+
+        it("destroys the override client when explicitly setting the client to undefined", async () => {
+          const mockOverrideClient = createMockClient();
+          service.setClient(userId, mockOverrideClient);
+          const userClientTracker = new ObservableTracker(service.userClient$(userId), false);
+          await userClientTracker.pauseUntilReceived(1);
+
+          service.setClient(userId, undefined);
+          await userClientTracker.expectCompletion();
+
+          expect(mockOverrideClient.free).toHaveBeenCalled();
+        });
       });
     });
   });
 });
+
+function createMockClient(): MockProxy<BitwardenClient> {
+  const client = mock<BitwardenClient>();
+  client.crypto.mockReturnValue(mock());
+  return client;
+}
diff --git a/libs/common/src/platform/services/sdk/default-sdk.service.ts b/libs/common/src/platform/services/sdk/default-sdk.service.ts
index 516334c7fb4..7e373faed48 100644
--- a/libs/common/src/platform/services/sdk/default-sdk.service.ts
+++ b/libs/common/src/platform/services/sdk/default-sdk.service.ts
@@ -1,5 +1,3 @@
-// FIXME: Update this file to be type safe and remove this and next line
-// @ts-strict-ignore
 import {
   combineLatest,
   concatMap,
@@ -10,6 +8,10 @@ import {
   tap,
   switchMap,
   catchError,
+  BehaviorSubject,
+  of,
+  takeWhile,
+  throwIfEmpty,
 } from "rxjs";
 
 import { KeyService, KdfConfigService, KdfConfig, KdfType } from "@bitwarden/key-management";
@@ -28,12 +30,19 @@ import { UserKey } from "../../../types/key";
 import { Environment, EnvironmentService } from "../../abstractions/environment.service";
 import { PlatformUtilsService } from "../../abstractions/platform-utils.service";
 import { SdkClientFactory } from "../../abstractions/sdk/sdk-client-factory";
-import { SdkService } from "../../abstractions/sdk/sdk.service";
+import { SdkService, UserNotLoggedInError } from "../../abstractions/sdk/sdk.service";
 import { compareValues } from "../../misc/compare-values";
 import { Rc } from "../../misc/reference-counting/rc";
 import { EncryptedString } from "../../models/domain/enc-string";
 
+// A symbol that represents an overriden client that is explicitly set to undefined,
+// blocking the creation of an internal client for that user.
+const UnsetClient = Symbol("UnsetClient");
+
 export class DefaultSdkService implements SdkService {
+  private sdkClientOverrides = new BehaviorSubject<{
+    [userId: UserId]: Rc<BitwardenClient> | typeof UnsetClient;
+  }>({});
   private sdkClientCache = new Map<UserId, Observable<Rc<BitwardenClient>>>();
 
   client$ = this.environmentService.environment$.pipe(
@@ -56,13 +65,54 @@ export class DefaultSdkService implements SdkService {
     private accountService: AccountService,
     private kdfConfigService: KdfConfigService,
     private keyService: KeyService,
-    private userAgent: string = null,
+    private userAgent: string | null = null,
   ) {}
 
   userClient$(userId: UserId): Observable<Rc<BitwardenClient> | undefined> {
-    // TODO: Figure out what happens when the user logs out
-    if (this.sdkClientCache.has(userId)) {
-      return this.sdkClientCache.get(userId);
+    return this.sdkClientOverrides.pipe(
+      takeWhile((clients) => clients[userId] !== UnsetClient, false),
+      map((clients) => {
+        if (clients[userId] === UnsetClient) {
+          throw new Error("Encountered UnsetClient even though it should have been filtered out");
+        }
+        return clients[userId] as Rc<BitwardenClient>;
+      }),
+      distinctUntilChanged(),
+      switchMap((clientOverride) => {
+        if (clientOverride) {
+          return of(clientOverride);
+        }
+
+        return this.internalClient$(userId);
+      }),
+      throwIfEmpty(() => new UserNotLoggedInError(userId)),
+    );
+  }
+
+  setClient(userId: UserId, client: BitwardenClient | undefined) {
+    const previousValue = this.sdkClientOverrides.value[userId];
+
+    this.sdkClientOverrides.next({
+      ...this.sdkClientOverrides.value,
+      [userId]: client ? new Rc(client) : UnsetClient,
+    });
+
+    if (previousValue !== UnsetClient && previousValue !== undefined) {
+      previousValue.markForDisposal();
+    }
+  }
+
+  /**
+   * This method is used to create a client for a specific user by using the existing state of the application.
+   * This methods is a fallback for when no client has been provided by Auth. As Auth starts implementing the
+   * client creation, this method will be deprecated.
+   * @param userId The user id for which to create the client
+   * @returns An observable that emits the client for the user
+   */
+  private internalClient$(userId: UserId): Observable<Rc<BitwardenClient> | undefined> {
+    const cached = this.sdkClientCache.get(userId);
+    if (cached !== undefined) {
+      return cached;
     }
 
     const account$ = this.accountService.accounts$.pipe(
@@ -91,7 +141,7 @@ export class DefaultSdkService implements SdkService {
         // Create our own observable to be able to implement clean-up logic
         return new Observable<Rc<BitwardenClient>>((subscriber) => {
           const createAndInitializeClient = async () => {
-            if (privateKey == null || userKey == null) {
+            if (env == null || kdfParams == null || privateKey == null || userKey == null) {
               return undefined;
             }
 
@@ -103,10 +153,11 @@ export class DefaultSdkService implements SdkService {
             return client;
           };
 
-          let client: Rc<BitwardenClient>;
+          let client: Rc<BitwardenClient> | undefined;
           createAndInitializeClient()
             .then((c) => {
               client = c === undefined ? undefined : new Rc(c);
+
               subscriber.next(client);
             })
             .catch((e) => {