diff --git a/keyserver/src/socket/tunnelbroker.js b/keyserver/src/socket/tunnelbroker.js
--- a/keyserver/src/socket/tunnelbroker.js
+++ b/keyserver/src/socket/tunnelbroker.js
@@ -2,12 +2,14 @@
 
 import WebSocket from 'ws';
 
+import { type ConnectionInitializationMessage } from 'lib/types/tunnelbroker-messages.js';
+
 function createTunnelbrokerWebsocket() {
   try {
     const tunnelbrokerSocket = new WebSocket('ws://localhost:51001');
     tunnelbrokerSocket.on('open', () => {
       // TODO: Replace keyserver details with actual details
-      const message = {
+      const message: ConnectionInitializationMessage = {
         type: 'sessionRequest',
         accessToken: 'foobar',
         deviceId: 'foo',
diff --git a/lib/types/tunnelbroker-messages.js b/lib/types/tunnelbroker-messages.js
new file mode 100644
--- /dev/null
+++ b/lib/types/tunnelbroker-messages.js
@@ -0,0 +1,9 @@
+// @flow
+
+export type TBConnectionInitializationMessage = {
+  +type: 'sessionRequest',
+  +deviceID: string,
+  +accessToken: string,
+  +notifyToken?: string,
+  +deviceType: 'mobile' | 'web' | 'keyserver',
+};
diff --git a/services/tunnelbroker/src/websockets/mod.rs b/services/tunnelbroker/src/websockets/mod.rs
--- a/services/tunnelbroker/src/websockets/mod.rs
+++ b/services/tunnelbroker/src/websockets/mod.rs
@@ -83,7 +83,7 @@
   tx: &tokio::sync::mpsc::UnboundedSender<std::string::String>,
 ) -> Result<(), serde_json::Error> {
   match serde_json::from_str::<Messages>(message)? {
-    Messages::SessionRequest(session_info) => {
+    Messages::ConnectionInitializationMessage(session_info) => {
       ACTIVE_CONNECTIONS.insert(session_info.device_id, tx.clone());
     }
     _ => {
diff --git a/shared/tunnelbroker_messages/src/messages/mod.rs b/shared/tunnelbroker_messages/src/messages/mod.rs
--- a/shared/tunnelbroker_messages/src/messages/mod.rs
+++ b/shared/tunnelbroker_messages/src/messages/mod.rs
@@ -11,5 +11,5 @@
 #[serde(untagged)]
 pub enum Messages {
   RefreshKeysRequest(RefreshKeyRequest),
-  SessionRequest(SessionRequest),
+  ConnectionInitializationMessage(ConnectionInitializationMessage),
 }
diff --git a/shared/tunnelbroker_messages/src/messages/session.rs b/shared/tunnelbroker_messages/src/messages/session.rs
--- a/shared/tunnelbroker_messages/src/messages/session.rs
+++ b/shared/tunnelbroker_messages/src/messages/session.rs
@@ -3,7 +3,7 @@
 use serde::{Deserialize, Serialize};
 
 /// The workflow when estabilishing a tunnelbroker connection:
-///   - Client sends SessionRequest
+///   - Client sends ConnectionInitializationMessage
 ///   - Tunnelbroker validates access_token with identity service
 ///   - Tunnelbroker emits an AMQP message declaring that it has opened a new
 ///     connection with a given device, so that the respective tunnelbroker
@@ -31,7 +31,7 @@
 /// service before continuing with the request.
 #[derive(Serialize, Deserialize)]
 #[serde(tag = "type", rename_all = "camelCase")]
-pub struct SessionRequest {
+pub struct ConnectionInitializationMessage {
   pub device_id: String,
   pub access_token: String,
   pub notify_token: Option<String>,
@@ -41,7 +41,7 @@
 }
 
 #[derive(Serialize, Deserialize)]
-pub struct SessionResponse {
+pub struct ConnectionInitializationResponse {
   pub session_id: String,
 }
 
@@ -59,7 +59,8 @@
     }"#;
 
     let request =
-      serde_json::from_str::<SessionRequest>(example_payload).unwrap();
+      serde_json::from_str::<ConnectionInitializationMessage>(example_payload)
+        .unwrap();
     assert_eq!(request.device_id, "foo");
     assert_eq!(request.access_token, "xkdeifjsld");
     assert_eq!(request.device_os, None);