diff --git a/keyserver/src/creators/account-creator.js b/keyserver/src/creators/account-creator.js
--- a/keyserver/src/creators/account-creator.js
+++ b/keyserver/src/creators/account-creator.js
@@ -236,6 +236,7 @@
     createNewUserCookie(id, {
       platformDetails: request.platformDetails,
       deviceToken,
+      primaryIdentityPublicKey: request.primaryIdentityPublicKey,
     }),
     deleteCookie(viewer.cookieID),
     dbQuery(newUserQuery),
diff --git a/keyserver/src/responders/user-responders.js b/keyserver/src/responders/user-responders.js
--- a/keyserver/src/responders/user-responders.js
+++ b/keyserver/src/responders/user-responders.js
@@ -203,6 +203,7 @@
   input: any,
   userID: string,
   calendarQuery: ?CalendarQuery,
+  primaryIdentityPublicKey?: ?string,
 ): Promise<LogInResponse> {
   const request: LogInRequest = input;
   const newServerTime = Date.now();
@@ -213,6 +214,7 @@
     createNewUserCookie(userID, {
       platformDetails: request.platformDetails,
       deviceToken,
+      primaryIdentityPublicKey,
     }),
     deleteCookie(viewer.cookieID),
   ]);
@@ -398,7 +400,13 @@
   }
 
   // 6. Complete login with call to `processSuccessfulLogin(...)`.
-  return await processSuccessfulLogin(viewer, input, userID, calendarQuery);
+  return await processSuccessfulLogin(
+    viewer,
+    input,
+    userID,
+    calendarQuery,
+    primaryIdentityPublicKey,
+  );
 }
 
 const updatePasswordRequestInputValidator = tShape({
diff --git a/keyserver/src/session/cookies.js b/keyserver/src/session/cookies.js
--- a/keyserver/src/session/cookies.js
+++ b/keyserver/src/session/cookies.js
@@ -644,6 +644,7 @@
 type UserCookieCreationParams = {
   platformDetails: PlatformDetails,
   deviceToken?: ?string,
+  primaryIdentityPublicKey?: ?string,
 };
 
 // The result of this function should never be passed directly to the Viewer
@@ -657,7 +658,7 @@
   userID: string,
   params: UserCookieCreationParams,
 ): Promise<UserViewerData> {
-  const { platformDetails, deviceToken } = params;
+  const { platformDetails, deviceToken, primaryIdentityPublicKey } = params;
   const { platform, ...versions } = platformDetails || defaultPlatformDetails;
   const versionsString =
     Object.keys(versions).length > 0 ? JSON.stringify(versions) : null;
@@ -679,10 +680,11 @@
     time,
     deviceToken,
     versionsString,
+    primaryIdentityPublicKey,
   ];
   const query = SQL`
     INSERT INTO cookies(id, hash, user, platform, creation_time, last_used,
-      device_token, versions)
+      device_token, versions, public_key)
     VALUES ${[cookieRow]}
   `;
   await dbQuery(query);