diff --git a/packages/backend/server/src/__tests__/auth/controller.spec.ts b/packages/backend/server/src/__tests__/auth/controller.spec.ts
index 8366462d4..a38cbaa26 100644
--- a/packages/backend/server/src/__tests__/auth/controller.spec.ts
+++ b/packages/backend/server/src/__tests__/auth/controller.spec.ts
@@ -264,6 +264,23 @@ test('should be able to sign out when duplicated csrf cookies exist', async t =>
   t.falsy(sessionRes.body.user);
 });
 
+test('should be able to sign out via GET /api/auth/sign-out (deprecated)', async t => {
+  const { app } = t.context;
+
+  const u1 = await app.createUser('u1@affine.pro');
+
+  await app
+    .POST('/api/auth/sign-in')
+    .send({ email: u1.email, password: u1.password })
+    .expect(200);
+
+  const res = await app.GET('/api/auth/sign-out').expect(200);
+  t.is(res.headers.deprecation, 'true');
+
+  const session = await currentUser(app);
+  t.falsy(session);
+});
+
 test('should reject sign out when csrf token mismatched', async t => {
   const { app } = t.context;
 
diff --git a/packages/backend/server/src/core/auth/controller.ts b/packages/backend/server/src/core/auth/controller.ts
index fe02cf38e..af8940d7d 100644
--- a/packages/backend/server/src/core/auth/controller.ts
+++ b/packages/backend/server/src/core/auth/controller.ts
@@ -228,6 +228,30 @@ export class AuthController {
     });
   }
 
+  @Public()
+  /**
+   * @deprecated Kept for 0.25 clients that still call GET `/api/auth/sign-out`.
+   * Use POST `/api/auth/sign-out` instead.
+   */
+  @Get('/sign-out')
+  async signOutDeprecated(
+    @Res() res: Response,
+    @Session() session: Session | undefined,
+    @Query('user_id') userId: string | undefined
+  ) {
+    res.setHeader('Deprecation', 'true');
+
+    if (!session) {
+      res.status(HttpStatus.OK).send({});
+      return;
+    }
+
+    await this.auth.signOut(session.sessionId, userId);
+    await this.auth.refreshCookies(res, session.sessionId);
+
+    res.status(HttpStatus.OK).send({});
+  }
+
   @Public()
   @Post('/sign-out')
   async signOut(
diff --git a/packages/frontend/core/src/__tests__/auth-client-nonce.spec.ts b/packages/frontend/core/src/__tests__/auth-client-nonce.spec.ts
new file mode 100644
index 000000000..6968920e5
--- /dev/null
+++ b/packages/frontend/core/src/__tests__/auth-client-nonce.spec.ts
@@ -0,0 +1,60 @@
+import { AuthSession } from '@affine/core/modules/cloud/entities/session';
+import { AuthService } from '@affine/core/modules/cloud/services/auth';
+import { FetchService } from '@affine/core/modules/cloud/services/fetch';
+import { AuthStore } from '@affine/core/modules/cloud/stores/auth';
+import { GlobalDialogService } from '@affine/core/modules/dialogs/services/dialog';
+import { UrlService } from '@affine/core/modules/url/services/url';
+import { Framework } from '@toeverything/infra';
+import { of } from 'rxjs';
+import { describe, expect, test, vi } from 'vitest';
+
+describe('AuthService oauthPreflight', () => {
+  test('should always send client_nonce on web', async () => {
+    let nonce: string | undefined;
+
+    const fetch = vi.fn(async (_input: string, _init?: RequestInit) => {
+      return {
+        json: async () => ({ url: 'https://example.com' }),
+      } as any;
+    });
+
+    const framework = new Framework();
+
+    framework.entity(
+      AuthSession,
+      () =>
+        ({
+          account$: of(null),
+          revalidate: vi.fn(),
+        }) as any
+    );
+    framework.service(FetchService, { fetch } as any);
+    framework.store(AuthStore, {
+      getClientNonce: () => nonce,
+      setClientNonce: (n: string) => {
+        nonce = n;
+      },
+    } as any);
+    framework.service(UrlService, { getClientScheme: () => null } as any);
+    framework.service(GlobalDialogService, { open: vi.fn() } as any);
+
+    framework.service(AuthService, [
+      FetchService,
+      AuthStore,
+      UrlService,
+      GlobalDialogService,
+    ]);
+
+    const auth = framework.provider().get(AuthService);
+    await auth.oauthPreflight('Google' as any, 'web');
+
+    expect(fetch).toHaveBeenCalledOnce();
+    const [, init] = fetch.mock.calls[0] as [
+      string,
+      (RequestInit & { body?: string })?,
+    ];
+    const body = JSON.parse(init?.body ?? '{}') as Record<string, unknown>;
+    expect(body.client_nonce).toBeTypeOf('string');
+    expect((body.client_nonce as string).length).toBeGreaterThan(0);
+  });
+});
diff --git a/packages/frontend/core/src/modules/cloud/services/auth.ts b/packages/frontend/core/src/modules/cloud/services/auth.ts
index afabd9abd..15822be2b 100644
--- a/packages/frontend/core/src/modules/cloud/services/auth.ts
+++ b/packages/frontend/core/src/modules/cloud/services/auth.ts
@@ -63,7 +63,11 @@ export class AuthService extends Service {
     redirectUrl?: string // url to redirect to after signed-in
   ) {
     track.$.$.auth.signIn({ method: 'magic-link' });
-    this.setClientNonce();
+    // Only native clients use `client_nonce` for magic-link/otp sign-in.
+    // Web needs to keep cross-device magic-link compatibility.
+    const magicLinkClientNonce = BUILD_CONFIG.isNative
+      ? this.setClientNonce()
+      : undefined;
     try {
       const scheme = this.urlService.getClientScheme();
       const magicLinkUrlParams = new URLSearchParams();
@@ -80,7 +84,7 @@ export class AuthService extends Service {
           // we call it [callbackUrl] instead of [redirect_uri]
           // to make it clear the url is used to finish the sign-in process instead of redirect after signed-in
           callbackUrl: `/magic-link?${magicLinkUrlParams.toString()}`,
-          client_nonce: this.store.getClientNonce(),
+          client_nonce: magicLinkClientNonce,
         }),
         headers: {
           'content-type': 'application/json',
@@ -117,7 +121,8 @@ export class AuthService extends Service {
     client: string,
     /** @deprecated*/ redirectUrl?: string
   ): Promise<Record<string, string>> {
-    this.setClientNonce();
+    // OAuth callback requires `client_nonce` for all clients (including web).
+    const clientNonce = this.setClientNonce();
     try {
       const res = await this.fetchService.fetch('/api/oauth/preflight', {
         method: 'POST',
@@ -125,7 +130,7 @@ export class AuthService extends Service {
           provider,
           client,
           redirect_uri: redirectUrl,
-          client_nonce: this.store.getClientNonce(),
+          client_nonce: clientNonce,
         }),
         headers: {
           'content-type': 'application/json',
@@ -241,10 +246,9 @@ export class AuthService extends Service {
     return headers;
   }
 
-  private setClientNonce() {
-    if (BUILD_CONFIG.isNative) {
-      // send random client nonce on native app
-      this.store.setClientNonce(nanoid());
-    }
+  private setClientNonce(): string {
+    const nonce = nanoid();
+    this.store.setClientNonce(nonce);
+    return nonce;
   }
 }