diff --git a/keyserver/src/session/cookies.js b/keyserver/src/session/cookies.js
index 19d995ec7..903b42858 100644
--- a/keyserver/src/session/cookies.js
+++ b/keyserver/src/session/cookies.js
@@ -1,860 +1,877 @@
 // @flow
 
 import crypto from 'crypto';
 import type { $Response, $Request } from 'express';
 import invariant from 'invariant';
 import bcrypt from 'twin-bcrypt';
 import url from 'url';
 
 import { hasMinCodeVersion } from 'lib/shared/version-utils.js';
 import type { Shape } from 'lib/types/core.js';
 import type { SignedIdentityKeysBlob } from 'lib/types/crypto-types.js';
 import { isWebPlatform } from 'lib/types/device-types.js';
 import type { Platform, PlatformDetails } from 'lib/types/device-types.js';
 import type { CalendarQuery } from 'lib/types/entry-types.js';
 import {
   type ServerSessionChange,
   cookieLifetime,
   cookieSources,
   type CookieSource,
   cookieTypes,
   sessionIdentifierTypes,
   type SessionIdentifierType,
 } from 'lib/types/session-types.js';
 import type { SIWESocialProof } from 'lib/types/siwe-types.js';
 import type { InitialClientSocketMessage } from 'lib/types/socket-types.js';
 import type { UserInfo } from 'lib/types/user-types.js';
 import { values } from 'lib/utils/objects.js';
 import { promiseAll } from 'lib/utils/promises.js';
 
 import { Viewer } from './viewer.js';
 import type { AnonymousViewerData, UserViewerData } from './viewer.js';
 import createIDs from '../creators/id-creator.js';
 import { createSession } from '../creators/session-creator.js';
 import { dbQuery, SQL } from '../database/database.js';
 import { deleteCookie } from '../deleters/cookie-deleters.js';
 import { handleAsyncPromise } from '../responders/handlers.js';
 import { clearDeviceToken } from '../updaters/device-token-updaters.js';
 import { updateThreadMembers } from '../updaters/thread-updaters.js';
 import { assertSecureRequest } from '../utils/security-utils.js';
 import {
   type AppURLFacts,
   getAppURLFactsFromRequestURL,
 } from '../utils/urls.js';
 
 function cookieIsExpired(lastUsed: number) {
   return lastUsed + cookieLifetime <= Date.now();
 }
 
 type SessionParameterInfo = {
   isSocket: boolean,
   sessionID: ?string,
   sessionIdentifierType: SessionIdentifierType,
   ipAddress: string,
   userAgent: ?string,
 };
 
 type FetchViewerResult =
   | { type: 'valid', viewer: Viewer }
   | InvalidFetchViewerResult;
 
 type InvalidFetchViewerResult =
   | {
       type: 'nonexistant',
       cookieName: ?string,
       cookieSource: ?CookieSource,
       sessionParameterInfo: SessionParameterInfo,
     }
   | {
       type: 'invalidated',
       cookieName: string,
       cookieID: string,
       cookieSource: CookieSource,
       sessionParameterInfo: SessionParameterInfo,
       platformDetails: ?PlatformDetails,
       deviceToken: ?string,
     };
 
 async function fetchUserViewer(
   cookie: string,
   cookieSource: CookieSource,
   sessionParameterInfo: SessionParameterInfo,
 ): Promise<FetchViewerResult> {
   const [cookieID, cookiePassword] = cookie.split(':');
   if (!cookieID || !cookiePassword) {
     return {
       type: 'nonexistant',
       cookieName: cookieTypes.USER,
       cookieSource,
       sessionParameterInfo,
     };
   }
 
   const query = SQL`
     SELECT hash, user, last_used, platform, device_token, versions
     FROM cookies
     WHERE id = ${cookieID} AND user IS NOT NULL
   `;
   const [[result], allSessionInfo] = await Promise.all([
     dbQuery(query),
     fetchSessionInfo(sessionParameterInfo, cookieID),
   ]);
   if (result.length === 0) {
     return {
       type: 'nonexistant',
       cookieName: cookieTypes.USER,
       cookieSource,
       sessionParameterInfo,
     };
   }
 
   let sessionID = null,
     sessionInfo = null;
   if (allSessionInfo) {
     ({ sessionID, ...sessionInfo } = allSessionInfo);
   }
 
   const cookieRow = result[0];
   let platformDetails = null;
   if (cookieRow.versions) {
     const versions = JSON.parse(cookieRow.versions);
     platformDetails = {
       platform: cookieRow.platform,
       codeVersion: versions.codeVersion,
       stateVersion: versions.stateVersion,
     };
   } else {
     platformDetails = { platform: cookieRow.platform };
   }
   const deviceToken = cookieRow.device_token;
 
   if (
     !bcrypt.compareSync(cookiePassword, cookieRow.hash) ||
     cookieIsExpired(cookieRow.last_used)
   ) {
     return {
       type: 'invalidated',
       cookieName: cookieTypes.USER,
       cookieID,
       cookieSource,
       sessionParameterInfo,
       platformDetails,
       deviceToken,
     };
   }
   const userID = cookieRow.user.toString();
   const viewer = new Viewer({
     isSocket: sessionParameterInfo.isSocket,
     loggedIn: true,
     id: userID,
     platformDetails,
     deviceToken,
     userID,
     cookieSource,
     cookieID,
     cookiePassword,
     sessionIdentifierType: sessionParameterInfo.sessionIdentifierType,
     sessionID,
     sessionInfo,
     isScriptViewer: false,
     ipAddress: sessionParameterInfo.ipAddress,
     userAgent: sessionParameterInfo.userAgent,
   });
   return { type: 'valid', viewer };
 }
 
 async function fetchAnonymousViewer(
   cookie: string,
   cookieSource: CookieSource,
   sessionParameterInfo: SessionParameterInfo,
 ): Promise<FetchViewerResult> {
   const [cookieID, cookiePassword] = cookie.split(':');
   if (!cookieID || !cookiePassword) {
     return {
       type: 'nonexistant',
       cookieName: cookieTypes.ANONYMOUS,
       cookieSource,
       sessionParameterInfo,
     };
   }
 
   const query = SQL`
     SELECT last_used, hash, platform, device_token, versions
     FROM cookies
     WHERE id = ${cookieID} AND user IS NULL
   `;
   const [[result], allSessionInfo] = await Promise.all([
     dbQuery(query),
     fetchSessionInfo(sessionParameterInfo, cookieID),
   ]);
   if (result.length === 0) {
     return {
       type: 'nonexistant',
       cookieName: cookieTypes.ANONYMOUS,
       cookieSource,
       sessionParameterInfo,
     };
   }
 
   let sessionID = null,
     sessionInfo = null;
   if (allSessionInfo) {
     ({ sessionID, ...sessionInfo } = allSessionInfo);
   }
 
   const cookieRow = result[0];
   let platformDetails = null;
   if (cookieRow.platform && cookieRow.versions) {
     const versions = JSON.parse(cookieRow.versions);
     platformDetails = {
       platform: cookieRow.platform,
       codeVersion: versions.codeVersion,
       stateVersion: versions.stateVersion,
     };
   } else if (cookieRow.platform) {
     platformDetails = { platform: cookieRow.platform };
   }
   const deviceToken = cookieRow.device_token;
 
   if (
     !bcrypt.compareSync(cookiePassword, cookieRow.hash) ||
     cookieIsExpired(cookieRow.last_used)
   ) {
     return {
       type: 'invalidated',
       cookieName: cookieTypes.ANONYMOUS,
       cookieID,
       cookieSource,
       sessionParameterInfo,
       platformDetails,
       deviceToken,
     };
   }
   const viewer = new Viewer({
     isSocket: sessionParameterInfo.isSocket,
     loggedIn: false,
     id: cookieID,
     platformDetails,
     deviceToken,
     cookieSource,
     cookieID,
     cookiePassword,
     sessionIdentifierType: sessionParameterInfo.sessionIdentifierType,
     sessionID,
     sessionInfo,
     isScriptViewer: false,
     ipAddress: sessionParameterInfo.ipAddress,
     userAgent: sessionParameterInfo.userAgent,
   });
   return { type: 'valid', viewer };
 }
 
 type SessionInfo = {
   +sessionID: ?string,
   +lastValidated: number,
   +lastUpdate: number,
   +calendarQuery: CalendarQuery,
 };
 async function fetchSessionInfo(
   sessionParameterInfo: SessionParameterInfo,
   cookieID: string,
 ): Promise<?SessionInfo> {
   const { sessionID } = sessionParameterInfo;
   const session = sessionID !== undefined ? sessionID : cookieID;
   if (!session) {
     return null;
   }
   const query = SQL`
     SELECT query, last_validated, last_update
     FROM sessions
     WHERE id = ${session} AND cookie = ${cookieID}
   `;
   const [result] = await dbQuery(query);
   if (result.length === 0) {
     return null;
   }
   return {
     sessionID,
     lastValidated: result[0].last_validated,
     lastUpdate: result[0].last_update,
     calendarQuery: JSON.parse(result[0].query),
   };
 }
 
 // This function is meant to consume a cookie that has already been processed.
 // That means it doesn't have any logic to handle an invalid cookie, and it
 // doesn't update the cookie's last_used timestamp.
 async function fetchViewerFromCookieData(
   req: $Request,
   sessionParameterInfo: SessionParameterInfo,
 ): Promise<FetchViewerResult> {
   let viewerResult;
   const { user, anonymous } = req.cookies;
   if (user) {
     viewerResult = await fetchUserViewer(
       user,
       cookieSources.HEADER,
       sessionParameterInfo,
     );
   } else if (anonymous) {
     viewerResult = await fetchAnonymousViewer(
       anonymous,
       cookieSources.HEADER,
       sessionParameterInfo,
     );
   } else {
     return {
       type: 'nonexistant',
       cookieName: null,
       cookieSource: null,
       sessionParameterInfo,
     };
   }
 
   // We protect against CSRF attacks by making sure that on web,
   // non-GET requests cannot use a bare cookie for session identification
   if (viewerResult.type === 'valid') {
     const { viewer } = viewerResult;
     invariant(
       req.method === 'GET' ||
         viewer.sessionIdentifierType !== sessionIdentifierTypes.COOKIE_ID ||
         !isWebPlatform(viewer.platform),
       'non-GET request from web using sessionIdentifierTypes.COOKIE_ID',
     );
   }
 
   return viewerResult;
 }
 
 async function fetchViewerFromRequestBody(
   body: mixed,
   sessionParameterInfo: SessionParameterInfo,
 ): Promise<FetchViewerResult> {
   if (!body || typeof body !== 'object') {
     return {
       type: 'nonexistant',
       cookieName: null,
       cookieSource: null,
       sessionParameterInfo,
     };
   }
   const cookiePair = body.cookie;
   if (cookiePair === null || cookiePair === '') {
     return {
       type: 'nonexistant',
       cookieName: null,
       cookieSource: cookieSources.BODY,
       sessionParameterInfo,
     };
   }
   if (!cookiePair || typeof cookiePair !== 'string') {
     return {
       type: 'nonexistant',
       cookieName: null,
       cookieSource: null,
       sessionParameterInfo,
     };
   }
   const [type, cookie] = cookiePair.split('=');
   if (type === cookieTypes.USER && cookie) {
     return await fetchUserViewer(
       cookie,
       cookieSources.BODY,
       sessionParameterInfo,
     );
   } else if (type === cookieTypes.ANONYMOUS && cookie) {
     return await fetchAnonymousViewer(
       cookie,
       cookieSources.BODY,
       sessionParameterInfo,
     );
   }
   return {
     type: 'nonexistant',
     cookieName: null,
     cookieSource: null,
     sessionParameterInfo,
   };
 }
 
 function getRequestIPAddress(req: $Request) {
   const { proxy } = getAppURLFactsFromRequestURL(req.originalUrl);
   let ipAddress;
   if (proxy === 'none') {
     ipAddress = req.socket.remoteAddress;
   } else if (proxy === 'apache') {
     ipAddress = req.get('X-Forwarded-For');
   }
   invariant(ipAddress, 'could not determine requesting IP address');
   return ipAddress;
 }
 
 function getSessionParameterInfoFromRequestBody(
   req: $Request,
 ): SessionParameterInfo {
   const body = (req.body: any);
   let sessionID =
     body.sessionID !== undefined || req.method !== 'GET'
       ? body.sessionID
       : null;
   if (sessionID === '') {
     sessionID = null;
   }
   const sessionIdentifierType =
     req.method === 'GET' || sessionID !== undefined
       ? sessionIdentifierTypes.BODY_SESSION_ID
       : sessionIdentifierTypes.COOKIE_ID;
   return {
     isSocket: false,
     sessionID,
     sessionIdentifierType,
     ipAddress: getRequestIPAddress(req),
     userAgent: req.get('User-Agent'),
   };
 }
 
 async function fetchViewerForJSONRequest(req: $Request): Promise<Viewer> {
   assertSecureRequest(req);
   const sessionParameterInfo = getSessionParameterInfoFromRequestBody(req);
   let result = await fetchViewerFromRequestBody(req.body, sessionParameterInfo);
   if (
     result.type === 'nonexistant' &&
     (result.cookieSource === null || result.cookieSource === undefined)
   ) {
     result = await fetchViewerFromCookieData(req, sessionParameterInfo);
   }
   return await handleFetchViewerResult(result);
 }
 
 const webPlatformDetails = { platform: 'web' };
 async function fetchViewerForHomeRequest(req: $Request): Promise<Viewer> {
   assertSecureRequest(req);
   const sessionParameterInfo = getSessionParameterInfoFromRequestBody(req);
   const result = await fetchViewerFromCookieData(req, sessionParameterInfo);
   return await handleFetchViewerResult(result, webPlatformDetails);
 }
 
 async function fetchViewerForSocket(
   req: $Request,
   clientMessage: InitialClientSocketMessage,
 ): Promise<?Viewer> {
   assertSecureRequest(req);
   const { sessionIdentification } = clientMessage.payload;
   const { sessionID } = sessionIdentification;
   const sessionParameterInfo = {
     isSocket: true,
     sessionID,
     sessionIdentifierType:
       sessionID !== undefined
         ? sessionIdentifierTypes.BODY_SESSION_ID
         : sessionIdentifierTypes.COOKIE_ID,
     ipAddress: getRequestIPAddress(req),
     userAgent: req.get('User-Agent'),
   };
 
   let result = await fetchViewerFromRequestBody(
     clientMessage.payload.sessionIdentification,
     sessionParameterInfo,
   );
   if (
     result.type === 'nonexistant' &&
     (result.cookieSource === null || result.cookieSource === undefined)
   ) {
     result = await fetchViewerFromCookieData(req, sessionParameterInfo);
   }
   if (result.type === 'valid') {
     return result.viewer;
   }
 
   const promises = {};
   if (result.cookieSource === cookieSources.BODY) {
     // We initialize a socket's Viewer after the WebSocket handshake, since to
     // properly initialize the Viewer we need a bunch of data, but that data
     // can't be sent until after the handshake. Consequently, by the time we
     // know that a cookie may be invalid, we are no longer communicating via
     // HTTP, and have no way to set a new cookie for HEADER (web) clients.
     const platformDetails =
       result.type === 'invalidated' ? result.platformDetails : null;
     const deviceToken =
       result.type === 'invalidated' ? result.deviceToken : null;
     promises.anonymousViewerData = createNewAnonymousCookie({
       platformDetails,
       deviceToken,
     });
   }
   if (result.type === 'invalidated') {
     promises.deleteCookie = deleteCookie(result.cookieID);
   }
   const { anonymousViewerData } = await promiseAll(promises);
 
   if (!anonymousViewerData) {
     return null;
   }
 
   return createViewerForInvalidFetchViewerResult(result, anonymousViewerData);
 }
 
 async function handleFetchViewerResult(
   result: FetchViewerResult,
   inputPlatformDetails?: PlatformDetails,
 ) {
   if (result.type === 'valid') {
     return result.viewer;
   }
 
   let platformDetails = inputPlatformDetails;
   if (!platformDetails && result.type === 'invalidated') {
     platformDetails = result.platformDetails;
   }
   const deviceToken = result.type === 'invalidated' ? result.deviceToken : null;
 
   const [anonymousViewerData] = await Promise.all([
     createNewAnonymousCookie({ platformDetails, deviceToken }),
     result.type === 'invalidated' ? deleteCookie(result.cookieID) : null,
   ]);
 
   return createViewerForInvalidFetchViewerResult(result, anonymousViewerData);
 }
 
 function createViewerForInvalidFetchViewerResult(
   result: InvalidFetchViewerResult,
   anonymousViewerData: AnonymousViewerData,
 ): Viewer {
   // If a null cookie was specified in the request body, result.cookieSource
   // will still be BODY here. The only way it would be null or undefined here
   // is if there was no cookie specified in either the body or the header, in
   // which case we default to returning the new cookie in the response header.
   const cookieSource =
     result.cookieSource !== null && result.cookieSource !== undefined
       ? result.cookieSource
       : cookieSources.HEADER;
   const viewer = new Viewer({
     ...anonymousViewerData,
     cookieSource,
     sessionIdentifierType: result.sessionParameterInfo.sessionIdentifierType,
     isSocket: result.sessionParameterInfo.isSocket,
     ipAddress: result.sessionParameterInfo.ipAddress,
     userAgent: result.sessionParameterInfo.userAgent,
   });
   viewer.sessionChanged = true;
 
   // If cookieName is falsey, that tells us that there was no cookie specified
   // in the request, which means we can't be invalidating anything.
   if (result.cookieName) {
     viewer.cookieInvalidated = true;
     viewer.initialCookieName = result.cookieName;
   }
 
   return viewer;
 }
 
 function addSessionChangeInfoToResult(
   viewer: Viewer,
   res: $Response,
   result: Object,
   appURLFacts: AppURLFacts,
 ) {
   let threadInfos = {},
     userInfos = {};
   if (result.cookieChange) {
     ({ threadInfos, userInfos } = result.cookieChange);
   }
   let sessionChange;
   if (viewer.cookieInvalidated) {
     sessionChange = ({
       cookieInvalidated: true,
       threadInfos,
       userInfos: (values(userInfos).map(a => a): UserInfo[]),
       currentUserInfo: {
         id: viewer.cookieID,
         anonymous: true,
       },
     }: ServerSessionChange);
   } else {
     sessionChange = ({
       cookieInvalidated: false,
       threadInfos,
       userInfos: (values(userInfos).map(a => a): UserInfo[]),
     }: ServerSessionChange);
   }
   if (viewer.cookieSource === cookieSources.BODY) {
     sessionChange.cookie = viewer.cookiePairString;
   } else {
     addActualHTTPCookie(viewer, res, appURLFacts);
   }
   if (viewer.sessionIdentifierType === sessionIdentifierTypes.BODY_SESSION_ID) {
     sessionChange.sessionID = viewer.sessionID ? viewer.sessionID : null;
   }
   result.cookieChange = sessionChange;
 }
 
 type AnonymousCookieCreationParams = Shape<{
   +platformDetails: ?PlatformDetails,
   +deviceToken: ?string,
 }>;
 const defaultPlatformDetails = {};
 
 // The result of this function should not be passed directly to the Viewer
 // constructor. Instead, it should be passed to viewer.setNewCookie. There are
 // several fields on AnonymousViewerData that are not set by this function:
 // sessionIdentifierType, cookieSource, ipAddress, and userAgent. These
 // parameters all depend on the initial request. If the result of this function
 // is passed to the Viewer constructor directly, the resultant Viewer object
 // will throw whenever anybody attempts to access the relevant properties.
 async function createNewAnonymousCookie(
   params: AnonymousCookieCreationParams,
 ): Promise<AnonymousViewerData> {
   const { platformDetails, deviceToken } = params;
   const { platform, ...versions } = platformDetails || defaultPlatformDetails;
   const versionsString =
     Object.keys(versions).length > 0 ? JSON.stringify(versions) : null;
 
   const time = Date.now();
   const cookiePassword = crypto.randomBytes(32).toString('hex');
   const cookieHash = bcrypt.hashSync(cookiePassword);
   const [[id]] = await Promise.all([
     createIDs('cookies', 1),
     deviceToken ? clearDeviceToken(deviceToken) : undefined,
   ]);
 
   const cookieRow = [
     id,
     cookieHash,
     null,
     platform,
     time,
     time,
     deviceToken,
     versionsString,
   ];
   const query = SQL`
     INSERT INTO cookies(id, hash, user, platform, creation_time, last_used,
       device_token, versions)
     VALUES ${[cookieRow]}
   `;
   await dbQuery(query);
   return {
     loggedIn: false,
     id,
     platformDetails,
     deviceToken,
     cookieID: id,
     cookiePassword,
     sessionID: undefined,
     sessionInfo: null,
     cookieInsertedThisRequest: true,
     isScriptViewer: false,
   };
 }
 
 type UserCookieCreationParams = {
   +platformDetails: PlatformDetails,
   +deviceToken?: ?string,
   +socialProof?: ?SIWESocialProof,
   +signedIdentityKeysBlob?: ?SignedIdentityKeysBlob,
 };
 
 // The result of this function should never be passed directly to the Viewer
 // constructor. Instead, it should be passed to viewer.setNewCookie. There are
 // several fields on UserViewerData that are not set by this function:
 // sessionID, sessionIdentifierType, cookieSource, and ipAddress. These
 // parameters all depend on the initial request. If the result of this function
 // is passed to the Viewer constructor directly, the resultant Viewer object
 // will throw whenever anybody attempts to access the relevant properties.
 async function createNewUserCookie(
   userID: string,
   params: UserCookieCreationParams,
 ): Promise<UserViewerData> {
   const { platformDetails, deviceToken, socialProof, signedIdentityKeysBlob } =
     params;
   const { platform, ...versions } = platformDetails || defaultPlatformDetails;
   const versionsString =
     Object.keys(versions).length > 0 ? JSON.stringify(versions) : null;
 
   const time = Date.now();
   const cookiePassword = crypto.randomBytes(32).toString('hex');
   const cookieHash = bcrypt.hashSync(cookiePassword);
   const [[cookieID]] = await Promise.all([
     createIDs('cookies', 1),
     deviceToken ? clearDeviceToken(deviceToken) : undefined,
   ]);
 
   const cookieRow = [
     cookieID,
     cookieHash,
     userID,
     platform,
     time,
     time,
     deviceToken,
     versionsString,
     JSON.stringify(socialProof),
     signedIdentityKeysBlob ? JSON.stringify(signedIdentityKeysBlob) : null,
   ];
   const query = SQL`
     INSERT INTO cookies(id, hash, user, platform, creation_time, last_used,
       device_token, versions, social_proof, signed_identity_keys)
     VALUES ${[cookieRow]}
   `;
   await dbQuery(query);
   return {
     loggedIn: true,
     id: userID,
     platformDetails,
     deviceToken,
     userID,
     cookieID,
     sessionID: undefined,
     sessionInfo: null,
     cookiePassword,
     cookieInsertedThisRequest: true,
     isScriptViewer: false,
   };
 }
 
 // This gets called after createNewUserCookie and from websiteResponder. If the
 // Viewer's sessionIdentifierType is COOKIE_ID then the cookieID is used as the
 // session identifier; otherwise, a new ID is created for the session.
 async function setNewSession(
   viewer: Viewer,
   calendarQuery: CalendarQuery,
   initialLastUpdate: number,
 ): Promise<void> {
   if (viewer.sessionIdentifierType !== sessionIdentifierTypes.COOKIE_ID) {
     const [sessionID] = await createIDs('sessions', 1);
     viewer.setSessionID(sessionID);
   }
   await createSession(viewer, calendarQuery, initialLastUpdate);
 }
 
 async function extendCookieLifespan(cookieID: string) {
   const time = Date.now();
   const query = SQL`
     UPDATE cookies SET last_used = ${time} WHERE id = ${cookieID}
   `;
   await dbQuery(query);
 }
 
 function addCookieToJSONResponse(
   viewer: Viewer,
   res: $Response,
   result: Object,
   expectCookieInvalidation: boolean,
   appURLFacts: AppURLFacts,
 ) {
   if (expectCookieInvalidation) {
     viewer.cookieInvalidated = false;
   }
   if (!viewer.getData().cookieInsertedThisRequest) {
     handleAsyncPromise(extendCookieLifespan(viewer.cookieID));
   }
   if (viewer.sessionChanged) {
     addSessionChangeInfoToResult(viewer, res, result, appURLFacts);
   } else if (viewer.cookieSource !== cookieSources.BODY) {
     addActualHTTPCookie(viewer, res, appURLFacts);
   }
 }
 
 function addCookieToHomeResponse(
   viewer: Viewer,
   res: $Response,
   appURLFacts: AppURLFacts,
 ) {
   if (!viewer.getData().cookieInsertedThisRequest) {
     handleAsyncPromise(extendCookieLifespan(viewer.cookieID));
   }
   addActualHTTPCookie(viewer, res, appURLFacts);
 }
 
 function getCookieOptions(appURLFacts: AppURLFacts) {
   const { baseDomain, basePath, https } = appURLFacts;
   const domainAsURL = new url.URL(baseDomain);
   return {
     domain: domainAsURL.hostname,
     path: basePath,
     httpOnly: true,
     secure: https,
     maxAge: cookieLifetime,
     sameSite: 'Strict',
   };
 }
 
 function addActualHTTPCookie(
   viewer: Viewer,
   res: $Response,
   appURLFacts: AppURLFacts,
 ) {
   res.cookie(
     viewer.cookieName,
     viewer.cookieString,
     getCookieOptions(appURLFacts),
   );
   if (viewer.cookieName !== viewer.initialCookieName) {
     res.clearCookie(viewer.initialCookieName, getCookieOptions(appURLFacts));
   }
 }
 
 async function setCookieSignedIdentityKeysBlob(
   cookieID: string,
   signedIdentityKeysBlob: SignedIdentityKeysBlob,
 ) {
   const signedIdentityKeysStr = JSON.stringify(signedIdentityKeysBlob);
   const query = SQL`
     UPDATE cookies 
     SET signed_identity_keys = ${signedIdentityKeysStr}
     WHERE id = ${cookieID}
   `;
   await dbQuery(query);
 }
 
+// Returns `true` if row with `id = cookieID` exists AND
+// `signed_identity_keys` is `NULL`. Otherwise, returns `false`.
+async function isCookieMissingSignedIdentityKeysBlob(
+  cookieID: string,
+): Promise<boolean> {
+  const query = SQL`
+    SELECT signed_identity_keys
+    FROM cookies 
+    WHERE id = ${cookieID}
+  `;
+  const [queryResult] = await dbQuery(query);
+  return (
+    queryResult.length === 1 && queryResult[0].signed_identity_keys === null
+  );
+}
+
 async function setCookiePlatform(
   viewer: Viewer,
   platform: Platform,
 ): Promise<void> {
   const newPlatformDetails = { ...viewer.platformDetails, platform };
   viewer.setPlatformDetails(newPlatformDetails);
   const query = SQL`
     UPDATE cookies
     SET platform = ${platform}
     WHERE id = ${viewer.cookieID}
   `;
   await dbQuery(query);
 }
 
 async function setCookiePlatformDetails(
   viewer: Viewer,
   platformDetails: PlatformDetails,
 ): Promise<void> {
   if (
     hasMinCodeVersion(platformDetails, 70) &&
     !hasMinCodeVersion(viewer.platformDetails, 70)
   ) {
     await updateThreadMembers(viewer);
   }
 
   viewer.setPlatformDetails(platformDetails);
   const { platform, ...versions } = platformDetails;
   const versionsString =
     Object.keys(versions).length > 0 ? JSON.stringify(versions) : null;
   const query = SQL`
     UPDATE cookies
     SET platform = ${platform}, versions = ${versionsString}
     WHERE id = ${viewer.cookieID}
   `;
   await dbQuery(query);
 }
 
 export {
   fetchViewerForJSONRequest,
   fetchViewerForHomeRequest,
   fetchViewerForSocket,
   createNewAnonymousCookie,
   createNewUserCookie,
   setNewSession,
   extendCookieLifespan,
   addCookieToJSONResponse,
   addCookieToHomeResponse,
   setCookieSignedIdentityKeysBlob,
+  isCookieMissingSignedIdentityKeysBlob,
   setCookiePlatform,
   setCookiePlatformDetails,
 };