diff --git a/services/identity/src/service.rs b/services/identity/src/service.rs
--- a/services/identity/src/service.rs
+++ b/services/identity/src/service.rs
@@ -25,6 +25,7 @@
 
 pub use proto::identity_service_server::IdentityServiceServer;
 use proto::{
+  get_user_id_request::AuthType as ProtoAuthType,
   identity_service_server::IdentityService,
   login_request::Data::PakeLoginRequest,
   login_request::Data::WalletLoginRequest,
@@ -356,7 +357,40 @@
     &self,
     request: Request<GetUserIdRequest>,
   ) -> Result<Response<GetUserIdResponse>, Status> {
-    unimplemented!();
+    info!("Received GetUserID request: {:?}", request);
+    let message = request.into_inner();
+    let auth_type = match ProtoAuthType::from_i32(message.auth_type) {
+      Some(ProtoAuthType::Password) => AuthType::Password,
+      Some(ProtoAuthType::Wallet) => AuthType::Wallet,
+      None => {
+        error!(
+          "Unable to parse AuthType from message: {}",
+          message.auth_type
+        );
+        return Err(Status::invalid_argument("invalid message"));
+      }
+    };
+    let user_id = match self
+      .client
+      .get_user_id_from_user_info(message.user_info, auth_type)
+      .await
+    {
+      Ok(Some(user_id)) => user_id,
+      Ok(None) => return Err(Status::not_found("no user ID found")),
+      Err(Error::AwsSdk(DynamoDBError::InternalServerError(_)))
+      | Err(Error::AwsSdk(
+        DynamoDBError::ProvisionedThroughputExceededException(_),
+      ))
+      | Err(Error::AwsSdk(DynamoDBError::RequestLimitExceeded(_))) => {
+        return Err(Status::unavailable("please retry"))
+      }
+      Err(e) => {
+        error!("Encountered an unexpected error: {}", e);
+        return Err(Status::failed_precondition("unexpected error"));
+      }
+    };
+    let response = Response::new(GetUserIdResponse { user_id });
+    Ok(response)
   }
 }