diff --git a/src/auth/backchannel.ts b/src/auth/backchannel.ts
index fe161c913..55586bcc2 100644
--- a/src/auth/backchannel.ts
+++ b/src/auth/backchannel.ts
@@ -60,9 +60,11 @@ type LoginHint = {
  * @returns {string} - The login hint as a JSON string.
  */
 const getLoginHint = (userId: string, domain: string): string => {
+  // remove trailing '/' from domain, added later for uniformity
+  const trimmedDomain = domain.endsWith('/') ? domain.slice(0, -1) : domain;
   const loginHint: LoginHint = {
     format: 'iss_sub',
-    iss: `https://${domain}/`,
+    iss: `https://${trimmedDomain}/`,
     sub: `${userId}`,
   };
   return JSON.stringify(loginHint);
diff --git a/test/auth/backchannel.test.ts b/test/auth/backchannel.test.ts
new file mode 100644
index 000000000..fed050548
--- /dev/null
+++ b/test/auth/backchannel.test.ts
@@ -0,0 +1,286 @@
+import nock from 'nock';
+
+import { AuthorizeOptions, Backchannel } from '../../src/auth/backchannel.js';
+
+const opts = {
+  domain: 'test-domain.auth0.com',
+  clientId: 'test-client-id',
+  clientSecret: 'test-client-secret',
+};
+
+const jwtOpts = {
+  ...opts,
+  clientAssertion: 'test-client-assertion',
+  clientAssertionType: 'urn:ietf:params:oauth:client-assertion-type:jwt-bearer',
+};
+
+const mtlsOpts = {
+  ...opts,
+  clientCertificate: 'test-client-certificate',
+  clientCertificateCA: 'test-client-certificate-ca-verified',
+};
+
+describe('Backchannel', () => {
+  let backchannel: Backchannel;
+
+  beforeAll(() => {
+    backchannel = new Backchannel(opts);
+  });
+
+  beforeEach(() => {
+    nock.cleanAll();
+  });
+
+  describe('#authorize', () => {
+    it('should require a userId', async () => {
+      nock(`https://${opts.domain}`).post('/bc-authorize').reply(400, {
+        error: 'invalid_request',
+        error_description:
+          'login_hint parameter validation failed: "sub" contains unsupported format',
+      });
+
+      await expect(backchannel.authorize({} as AuthorizeOptions)).rejects.toThrow(
+        'login_hint parameter validation failed: "sub" contains unsupported format'
+      );
+    });
+
+    it('should require a binding_message', async () => {
+      nock(`https://${opts.domain}`).post('/bc-authorize').reply(400, {
+        error: 'invalid_request',
+        error_description: 'binding_message is required',
+      });
+
+      await expect(
+        backchannel.authorize({ userId: 'auth0|test-user-id' } as AuthorizeOptions)
+      ).rejects.toThrow('binding_message is required');
+    });
+
+    it('should require a valid openid scope', async () => {
+      nock(`https://${opts.domain}`).post('/bc-authorize').reply(400, {
+        error: 'invalid_scope',
+        error_description: 'openid scope must be requested',
+      });
+
+      await expect(
+        backchannel.authorize({
+          userId: 'auth0|test-user-id',
+          binding_message: 'Test binding message',
+          scope: 'invalid_scope',
+        } as AuthorizeOptions)
+      ).rejects.toThrow('openid scope must be requested');
+    });
+
+    it('should return authorization response', async () => {
+      nock(`https://${opts.domain}`).post('/bc-authorize').reply(200, {
+        auth_req_id: 'test-auth-req-id',
+        expires_in: 300,
+        interval: 5,
+      });
+
+      await expect(
+        backchannel.authorize({
+          userId: 'auth0|test-user-id',
+          binding_message: 'Test binding message',
+          scope: 'openid',
+        })
+      ).resolves.toMatchObject({
+        auth_req_id: 'test-auth-req-id',
+        expires_in: 300,
+        interval: 5,
+      });
+    });
+
+    it('should throw for invalid request', async () => {
+      nock(`https://${opts.domain}`).post('/bc-authorize').reply(400, {
+        error: 'invalid_request',
+        error_description: 'Invalid request parameters',
+      });
+
+      await expect(
+        backchannel.authorize({
+          userId: 'auth0|test-user-id',
+          binding_message: 'Test binding message',
+          scope: 'openid',
+        })
+      ).rejects.toThrowError(
+        expect.objectContaining({
+          body: expect.anything(),
+        })
+      );
+    });
+
+    it('should support Private Key JWT authentication', async () => {
+      const jwtBackchannel = new Backchannel(jwtOpts);
+
+      nock(`https://${opts.domain}`).post('/bc-authorize').reply(200, {
+        auth_req_id: 'test-auth-req-id',
+        expires_in: 300,
+        interval: 5,
+      });
+
+      await expect(
+        jwtBackchannel.authorize({
+          userId: 'auth0|test-user-id',
+          binding_message: 'Test binding message',
+          scope: 'openid',
+        })
+      ).resolves.toMatchObject({
+        auth_req_id: 'test-auth-req-id',
+        expires_in: 300,
+        interval: 5,
+      });
+    });
+
+    it('should support mTLS authentication', async () => {
+      const mtlsBackchannel = new Backchannel(mtlsOpts);
+
+      nock(`https://${opts.domain}`).post('/bc-authorize').reply(200, {
+        auth_req_id: 'test-auth-req-id',
+        expires_in: 300,
+        interval: 5,
+      });
+
+      await expect(
+        mtlsBackchannel.authorize({
+          userId: 'auth0|test-user-id',
+          binding_message: 'Test binding message',
+          scope: 'openid',
+        })
+      ).resolves.toMatchObject({
+        auth_req_id: 'test-auth-req-id',
+        expires_in: 300,
+        interval: 5,
+      });
+    });
+  });
+
+  describe('#backchannelGrant', () => {
+    it('should throw for invalid or expired auth_req_id', async () => {
+      nock(`https://${opts.domain}`).post('/oauth/token').reply(401, {
+        error: 'invalid_grant',
+        error_description: 'Invalid or expired auth_req_id',
+      });
+
+      await expect(
+        backchannel.backchannelGrant({
+          auth_req_id: 'invalid-auth-req-id',
+        })
+      ).rejects.toThrow('Invalid or expired auth_req_id');
+    });
+
+    it('should return token response', async () => {
+      nock(`https://${opts.domain}`).post('/oauth/token').reply(200, {
+        access_token: 'test-access-token',
+        id_token: 'test-id-token',
+        expires_in: 86400,
+        scope: 'openid',
+      });
+
+      await expect(
+        backchannel.backchannelGrant({
+          auth_req_id: 'test-auth-req-id',
+        })
+      ).resolves.toMatchObject({
+        access_token: 'test-access-token',
+        id_token: 'test-id-token',
+        expires_in: 86400,
+        scope: 'openid',
+      });
+    });
+
+    it('should throw for authorization pending', async () => {
+      nock(`https://${opts.domain}`).post('/oauth/token').reply(400, {
+        error: 'authorization_pending',
+        error_description: 'The end-user authorization is pending',
+      });
+
+      await expect(
+        backchannel.backchannelGrant({
+          auth_req_id: 'test-auth-req-id',
+        })
+      ).rejects.toThrowError(
+        expect.objectContaining({
+          body: expect.anything(),
+        })
+      );
+    });
+
+    it('should throw for access denied', async () => {
+      nock(`https://${opts.domain}`).post('/oauth/token').reply(400, {
+        error: 'access_denied',
+        error_description: 'The end-user denied the authorization request or it has been expired',
+      });
+
+      await expect(
+        backchannel.backchannelGrant({
+          auth_req_id: 'test-auth-req-id',
+        })
+      ).rejects.toThrowError(
+        expect.objectContaining({
+          body: expect.anything(),
+        })
+      );
+    });
+
+    it('should throw for polling too quickly', async () => {
+      nock(`https://${opts.domain}`).post('/oauth/token').reply(400, {
+        error: 'slow_down',
+        error_description: 'You are polling faster than allowed. Try again in 10 seconds.',
+      });
+
+      await expect(
+        backchannel.backchannelGrant({
+          auth_req_id: 'test-auth-req-id',
+        })
+      ).rejects.toThrowError(
+        expect.objectContaining({
+          body: expect.anything(),
+        })
+      );
+    });
+
+    it('should support Private Key JWT authentication', async () => {
+      const jwtBackchannel = new Backchannel(jwtOpts);
+
+      nock(`https://${opts.domain}`).post('/oauth/token').reply(200, {
+        access_token: 'test-access-token',
+        id_token: 'test-id-token',
+        expires_in: 86400,
+        scope: 'openid',
+      });
+
+      await expect(
+        jwtBackchannel.backchannelGrant({
+          auth_req_id: 'test-auth-req-id',
+        })
+      ).resolves.toMatchObject({
+        access_token: 'test-access-token',
+        id_token: 'test-id-token',
+        expires_in: 86400,
+        scope: 'openid',
+      });
+    });
+
+    it('should support mTLS authentication', async () => {
+      const mtlsBackchannel = new Backchannel(mtlsOpts);
+
+      nock(`https://${opts.domain}`).post('/oauth/token').reply(200, {
+        access_token: 'test-access-token',
+        id_token: 'test-id-token',
+        expires_in: 86400,
+        scope: 'openid',
+      });
+
+      await expect(
+        mtlsBackchannel.backchannelGrant({
+          auth_req_id: 'test-auth-req-id',
+        })
+      ).resolves.toMatchObject({
+        access_token: 'test-access-token',
+        id_token: 'test-id-token',
+        expires_in: 86400,
+        scope: 'openid',
+      });
+    });
+  });
+});