diff --git a/.gitignore b/.gitignore
index 78a1b31bb..c827a4749 100644
--- a/.gitignore
+++ b/.gitignore
@@ -130,3 +130,4 @@ dist
 # editor
 .vscode/
 .idea/
+.prettierrc
diff --git a/src/client/callers/authSignToken.ts b/src/client/callers/authSignToken.ts
new file mode 100644
index 000000000..34861e645
--- /dev/null
+++ b/src/client/callers/authSignToken.ts
@@ -0,0 +1,12 @@
+import type { HandlerTypes } from '@matrixai/rpc';
+import type AuthSignToken from '../handlers/AuthSignToken.js';
+import { UnaryCaller } from '@matrixai/rpc';
+
+type CallerTypes = HandlerTypes<AuthSignToken>;
+
+const authSignToken = new UnaryCaller<
+  CallerTypes['input'],
+  CallerTypes['output']
+>();
+
+export default authSignToken;
diff --git a/src/client/callers/index.ts b/src/client/callers/index.ts
index 560b3a4eb..d3aa78c8e 100644
--- a/src/client/callers/index.ts
+++ b/src/client/callers/index.ts
@@ -4,6 +4,7 @@ import agentStop from './agentStop.js';
 import agentUnlock from './agentUnlock.js';
 import auditEventsGet from './auditEventsGet.js';
 import auditMetricGet from './auditMetricGet.js';
+import authSignToken from './authSignToken.js';
 import gestaltsActionsGetByIdentity from './gestaltsActionsGetByIdentity.js';
 import gestaltsActionsGetByNode from './gestaltsActionsGetByNode.js';
 import gestaltsActionsSetByIdentity from './gestaltsActionsSetByIdentity.js';
@@ -85,6 +86,7 @@ const clientManifest = {
   agentUnlock,
   auditEventsGet,
   auditMetricGet,
+  authSignToken,
   gestaltsActionsGetByIdentity,
   gestaltsActionsGetByNode,
   gestaltsActionsSetByIdentity,
@@ -165,6 +167,7 @@ export {
   agentStop,
   agentUnlock,
   auditEventsGet,
+  authSignToken,
   gestaltsActionsGetByIdentity,
   gestaltsActionsGetByNode,
   gestaltsActionsSetByIdentity,
diff --git a/src/client/errors.ts b/src/client/errors.ts
index 24cee22b7..476b7a2e6 100644
--- a/src/client/errors.ts
+++ b/src/client/errors.ts
@@ -50,6 +50,13 @@ class ErrorClientVerificationFailed<T> extends ErrorClientService<T> {
   exitCode = sysexits.USAGE;
 }
 
+class ErrorAuthentication<T> extends ErrorPolykey<T> {}
+
+class ErrorAuthenticationInvalidToken<T> extends ErrorAuthentication<T> {
+  static description = 'Token is invalid';
+  exitCode = sysexits.PROTOCOL;
+}
+
 export {
   ErrorClient,
   ErrorClientAuthMissing,
@@ -62,4 +69,6 @@ export {
   ErrorClientServiceNotRunning,
   ErrorClientServiceDestroyed,
   ErrorClientVerificationFailed,
+  ErrorAuthentication,
+  ErrorAuthenticationInvalidToken,
 };
diff --git a/src/client/handlers/AuthSignToken.ts b/src/client/handlers/AuthSignToken.ts
new file mode 100644
index 000000000..04910b722
--- /dev/null
+++ b/src/client/handlers/AuthSignToken.ts
@@ -0,0 +1,59 @@
+import type {
+  ClientRPCRequestParams,
+  ClientRPCResponseResult,
+  IdentityRequestData,
+  IdentityResponseData,
+  TokenIdentityRequest,
+  TokenIdentityResponse,
+} from '../types.js';
+import type KeyRing from '../../keys/KeyRing.js';
+import type { PublicKey } from '../../keys/types.js';
+import { UnaryHandler } from '@matrixai/rpc';
+import Token from '../../tokens/Token.js';
+import * as clientErrors from '../errors.js';
+import * as nodesUtils from '../../nodes/utils.js';
+
+class AuthSignToken extends UnaryHandler<
+  {
+    keyRing: KeyRing;
+  },
+  ClientRPCRequestParams<TokenIdentityRequest>,
+  ClientRPCResponseResult<TokenIdentityResponse>
+> {
+  public handle = async (
+    input: ClientRPCRequestParams<TokenIdentityRequest>,
+  ): Promise<TokenIdentityResponse> => {
+    const { keyRing }: { keyRing: KeyRing } = this.container;
+
+    // Get and verify incoming node
+    const inputToken = { payload: input.payload, signatures: input.signatures };
+    const incomingToken = Token.fromEncoded<IdentityRequestData>(inputToken);
+    if (!('publicKey' in incomingToken.payload)) {
+      throw new clientErrors.ErrorAuthenticationInvalidToken(
+        'Input token does not contain public key',
+      );
+    }
+    const incomingPublicKey = Buffer.from(
+      incomingToken.payload.publicKey,
+      'base64url',
+    ) as PublicKey;
+    if (!incomingToken.verifyWithPublicKey(incomingPublicKey)) {
+      throw new clientErrors.ErrorAuthenticationInvalidToken(
+        'Incoming token does not match its signature',
+      );
+    }
+
+    // Create the outgoing token with the incoming token integrated into the
+    // payload.
+    const outgoingTokenPayload: IdentityResponseData = {
+      requestToken: inputToken,
+      nodeId: nodesUtils.encodeNodeId(keyRing.getNodeId()),
+    };
+    const outgoingToken =
+      Token.fromPayload<IdentityResponseData>(outgoingTokenPayload);
+    outgoingToken.signWithPrivateKey(keyRing.keyPair);
+    return outgoingToken.toEncoded();
+  };
+}
+
+export default AuthSignToken;
diff --git a/src/client/handlers/index.ts b/src/client/handlers/index.ts
index 037eb0318..d846ed093 100644
--- a/src/client/handlers/index.ts
+++ b/src/client/handlers/index.ts
@@ -22,6 +22,7 @@ import AgentStop from './AgentStop.js';
 import AgentUnlock from './AgentUnlock.js';
 import AuditEventsGet from './AuditEventsGet.js';
 import AuditMetricGet from './AuditMetricGet.js';
+import AuthSignToken from './AuthSignToken.js';
 import GestaltsActionsGetByIdentity from './GestaltsActionsGetByIdentity.js';
 import GestaltsActionsGetByNode from './GestaltsActionsGetByNode.js';
 import GestaltsActionsSetByIdentity from './GestaltsActionsSetByIdentity.js';
@@ -122,6 +123,7 @@ const serverManifest = (container: {
     agentUnlock: new AgentUnlock(container),
     auditEventsGet: new AuditEventsGet(container),
     auditMetricGet: new AuditMetricGet(container),
+    authSignToken: new AuthSignToken(container),
     gestaltsActionsGetByIdentity: new GestaltsActionsGetByIdentity(container),
     gestaltsActionsGetByNode: new GestaltsActionsGetByNode(container),
     gestaltsActionsSetByIdentity: new GestaltsActionsSetByIdentity(container),
@@ -208,6 +210,7 @@ export {
   AgentUnlock,
   AuditEventsGet,
   AuditMetricGet,
+  AuthSignToken,
   GestaltsActionsGetByIdentity,
   GestaltsActionsGetByNode,
   GestaltsActionsSetByIdentity,
diff --git a/src/client/types.ts b/src/client/types.ts
index 8e08254fe..e9900e89d 100644
--- a/src/client/types.ts
+++ b/src/client/types.ts
@@ -21,6 +21,7 @@ import type {
 } from '../keys/types.js';
 import type { Notification } from '../notifications/types.js';
 import type { ProviderToken } from '../identities/types.js';
+import type { TokenPayload, SignedTokenEncoded } from '../tokens/types.js';
 import type { AuditMetricGetTypeOverride } from './callers/auditMetricGet.js';
 import type {
   NodeContact,
@@ -107,6 +108,22 @@ type TokenMessage = {
   token: ProviderToken;
 };
 
+// Return URL must be present on the token, otherwise token contents is decided
+// by the client.
+type IdentityRequestData = TokenPayload & {
+  returnURL: string;
+  publicKey: string;
+};
+
+type TokenIdentityRequest = SignedTokenEncoded;
+
+type IdentityResponseData = TokenPayload & {
+  requestToken: TokenIdentityRequest;
+  nodeId: NodeIdEncoded;
+};
+
+type TokenIdentityResponse = SignedTokenEncoded;
+
 // Nodes messages
 
 type NodeIdMessage = {
@@ -405,6 +422,10 @@ export type {
   ClaimIdMessage,
   ClaimNodeMessage,
   TokenMessage,
+  IdentityRequestData,
+  IdentityResponseData,
+  TokenIdentityRequest,
+  TokenIdentityResponse,
   NodeIdMessage,
   AddressMessage,
   NodeAddressMessage,
diff --git a/src/network/utils.ts b/src/network/utils.ts
index 253d2bcb5..c6e252a97 100644
--- a/src/network/utils.ts
+++ b/src/network/utils.ts
@@ -477,7 +477,10 @@ function fromError(error: any) {
     // serialising only the error type, message and its stack.
     const wrappedError = new errors.ErrorPolykeyUnexpected(
       `Unexpected error occurred: ${error.name}`,
-      { cause: error },
+      {
+        cause: error,
+        data: { message: 'message' in error ? error.message : undefined },
+      },
     );
     return wrappedError.toJSON();
   }