diff --git a/keyserver/src/endpoints.js b/keyserver/src/endpoints.js
--- a/keyserver/src/endpoints.js
+++ b/keyserver/src/endpoints.js
@@ -150,6 +150,7 @@
   roleModificationResultValidator,
 } from './responders/thread-responders.js';
 import {
+  identityServiceOlmAuthRequestInputValidator,
   userSubscriptionUpdateResponder,
   passwordUpdateResponder,
   sendVerificationEmailResponder,
@@ -178,6 +179,7 @@
   updatePasswordRequestInputValidator,
   updateUserAvatarResponderValidator,
   updateUserSettingsInputValidator,
+  identityServiceOlmAuthResponder,
 } from './responders/user-responders.js';
 import {
   codeVerificationResponder,
@@ -533,6 +535,12 @@
     logInResponseValidator,
     [],
   ),
+  identity_service_olm_auth: createJSONResponder(
+    identityServiceOlmAuthResponder,
+    identityServiceOlmAuthRequestInputValidator,
+    logInResponseValidator,
+    [],
+  ),
   update_user_avatar: createJSONResponder(
     updateUserAvatarResponder,
     updateUserAvatarRequestValidator,
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
@@ -23,6 +23,7 @@
   UpdatePasswordRequest,
   UpdateUserSettingsRequest,
   PolicyAcknowledgmentRequest,
+  IdentityServiceOlmAuthRequest,
 } from 'lib/types/account-types.js';
 import {
   userSettingsTypes,
@@ -663,6 +664,29 @@
   });
 }
 
+const UserIdentifierValidator = t.refinement(
+  t.Object,
+  x =>
+    ('username' in x && !('walletAddress' in x)) ||
+    ('walletAddress' in x && !('username' in x)),
+);
+
+export const identityServiceOlmAuthRequestInputValidator: TInterface<IdentityServiceOlmAuthRequest> =
+  tShape<IdentityServiceOlmAuthRequest>({
+    identifier: UserIdentifierValidator,
+    signingPublicKey: t.String,
+    calendarQuery: entryQueryInputValidator,
+    deviceTokenUpdateRequest: t.maybe(deviceTokenUpdateRequestInputValidator),
+    platformDetails: tPlatformDetails,
+    watchedIDs: t.list(tID),
+    initialContentEncryptedMessage: t.String,
+    initialNotificationsEncryptedMessage: t.String,
+  });
+
+async function identityServiceOlmAuthResponder(): Promise<string> {
+  return 'UNIMPLEMENTED';
+}
+
 export const updatePasswordRequestInputValidator: TInterface<UpdatePasswordRequest> =
   tShape<UpdatePasswordRequest>({
     code: t.String,
@@ -744,4 +768,5 @@
   updateUserSettingsResponder,
   policyAcknowledgmentResponder,
   updateUserAvatarResponder,
+  identityServiceOlmAuthResponder,
 };
diff --git a/lib/actions/user-actions.js b/lib/actions/user-actions.js
--- a/lib/actions/user-actions.js
+++ b/lib/actions/user-actions.js
@@ -9,6 +9,7 @@
   RegisterInfo,
   UpdateUserSettingsRequest,
   PolicyAcknowledgmentRequest,
+  BaseIdentityServiceOlmAuthRequest,
 } from '../types/account-types.js';
 import type {
   UpdateUserAvatarRequest,
@@ -175,6 +176,34 @@
     };
   };
 
+const identityServiceOlmAuthActionTypes = Object.freeze({
+  started: 'IDENTITY_SERVICE_OLM_AUTH_STARTED',
+  success: 'IDENTITY_SERVICE_OLM_AUTH_SUCCESS',
+  failed: 'IDENTITY_SERVICE_OLM_AUTH_FAILED',
+});
+const identityServiceOlmAuth =
+  (
+    callServerEndpoint: CallServerEndpoint,
+  ): ((
+    baseIdentityServiceOlmAuthPayload: BaseIdentityServiceOlmAuthRequest,
+    options?: ?CallServerEndpointOptions,
+  ) => Promise<string>) =>
+  async (baseIdentityServiceOlmAuthPayload, options) => {
+    const watchedIDs = threadWatcher.getWatchedIDs();
+    const response = await callServerEndpoint(
+      'identity_service_olm_auth',
+      {
+        ...baseIdentityServiceOlmAuthPayload,
+        watchedIDs,
+        platformDetails: getConfig().platformDetails,
+      },
+      {
+        ...options,
+      },
+    );
+    return response;
+  };
+
 const changeUserPasswordActionTypes = Object.freeze({
   started: 'CHANGE_USER_PASSWORD_STARTED',
   success: 'CHANGE_USER_PASSWORD_SUCCESS',
@@ -353,4 +382,6 @@
   updateUserAvatar,
   resetUserStateActionType,
   setAccessTokenActionType,
+  identityServiceOlmAuth,
+  identityServiceOlmAuthActionTypes,
 };
diff --git a/lib/types/account-types.js b/lib/types/account-types.js
--- a/lib/types/account-types.js
+++ b/lib/types/account-types.js
@@ -159,6 +159,25 @@
   +notAcknowledgedPolicies?: $ReadOnlyArray<PolicyType>,
 };
 
+export type UserIdentifier =
+  | { username: string, walletAddress?: empty }
+  | { username?: empty, walletAddress: string };
+
+export type BaseIdentityServiceOlmAuthRequest = {
+  +identifier: UserIdentifier,
+  +signingPublicKey: string,
+  +calendarQuery: CalendarQuery,
+  +deviceTokenUpdateRequest?: ?DeviceTokenUpdateRequest,
+  +initialContentEncryptedMessage: string,
+  +initialNotificationsEncryptedMessage: string,
+};
+
+export type IdentityServiceOlmAuthRequest = {
+  ...BaseIdentityServiceOlmAuthRequest,
+  +watchedIDs: $ReadOnlyArray<string>,
+  +platformDetails: PlatformDetails,
+};
+
 export type UpdatePasswordRequest = {
   code: string,
   password: string,
diff --git a/lib/types/endpoints.js b/lib/types/endpoints.js
--- a/lib/types/endpoints.js
+++ b/lib/types/endpoints.js
@@ -93,6 +93,7 @@
   VERIFY_INVITE_LINK: 'verify_invite_link',
   SIWE_NONCE: 'siwe_nonce',
   SIWE_AUTH: 'siwe_auth',
+  IDENTITY_SERVICE_OLM_AUTH: 'identity_service_olm_auth',
   UPDATE_USER_AVATAR: 'update_user_avatar',
   UPLOAD_MEDIA_METADATA: 'upload_media_metadata',
   SEARCH_MESSAGES: 'search_messages',
diff --git a/lib/types/redux-types.js b/lib/types/redux-types.js
--- a/lib/types/redux-types.js
+++ b/lib/types/redux-types.js
@@ -952,6 +952,22 @@
       +payload: Error,
       +loadingInfo: LoadingInfo,
     }
+  | {
+      +type: 'IDENTITY_SERVICE_OLM_AUTH_STARTED',
+      +payload?: LogInStartingPayload,
+      +loadingInfo: LoadingInfo,
+    }
+  | {
+      +type: 'IDENTITY_SERVICE_OLM_AUTH_SUCCESS',
+      +payload?: LogInResult,
+      +loadingInfo: LoadingInfo,
+    }
+  | {
+      +type: 'IDENTITY_SERVICE_OLM_AUTH_FAILED',
+      +error: true,
+      +payload: Error,
+      +loadingInfo: LoadingInfo,
+    }
   | {
       +type: 'RECORD_NOTIF_PERMISSION_ALERT',
       +payload: { +time: number },