fix(api): adminCreateUser handles duplicate users

src/targets/adminCreateUser.test.ts

@@ -1,8 +1,10 @@
 import { ClockFake } from "../__tests__/clockFake";
 import { MockUserPoolClient } from "../__tests__/mockUserPoolClient";
 import { UUID } from "../__tests__/patterns";
+import { UsernameExistsError } from "../errors";
 import { CognitoClient } from "../services";
 import { AdminCreateUser, AdminCreateUserTarget } from "./adminCreateUser";
+import * as TDB from "../__tests__/testDataBuilder";
 
 describe("AdminCreateUser target", () => {
   let adminCreateUser: AdminCreateUserTarget;
@@ -52,7 +54,21 @@ describe("AdminCreateUser target", () => {
   it.todo("can create an alias to an existing user");
   it.todo("can resend the welcome message");
   it.todo("can suppress the welcome message");
-  it.todo("handles creating a duplicate user");
+
+  it("handles creating a duplicate user", async () => {
+    const existingUser = TDB.user();
+    MockUserPoolClient.getUserByUsername.mockResolvedValue(existingUser);
+
+    await expect(
+      adminCreateUser({
+        TemporaryPassword: "pwd",
+        UserAttributes: existingUser.Attributes,
+        Username: existingUser.Username,
+        UserPoolId: "test",
+      })
+    ).rejects.toEqual(new UsernameExistsError());
+  });
+
   it.todo("invokes the PreSignIn lambda");
   it.todo("saves a user with a generated temporary password");
   it.todo("sends a welcome message to the user");

src/targets/adminCreateUser.ts

@@ -3,7 +3,7 @@ import {
   AdminCreateUserResponse,
 } from "aws-sdk/clients/cognitoidentityserviceprovider";
 import uuid from "uuid";
-import { UnsupportedError } from "../errors";
+import { UnsupportedError, UsernameExistsError } from "../errors";
 import { Services } from "../services";
 import { attributesInclude, User } from "../services/userPoolClient";
 
@@ -22,6 +22,12 @@ export const AdminCreateUser = ({
   }
 
   const userPool = await cognitoClient.getUserPool(req.UserPoolId);
+  const existingUser = await userPool.getUserByUsername(req.Username);
+  if (existingUser && req.MessageAction === "RESEND") {
+    throw new UnsupportedError("AdminCreateUser with MessageAction=RESEND");
+  } else if (existingUser) {
+    throw new UsernameExistsError();
+  }
 
   const attributes = attributesInclude("sub", req.UserAttributes)
     ? req.UserAttributes ?? []
@@ -41,7 +47,7 @@ export const AdminCreateUser = ({
   };
   await userPool.saveUser(user);
 
-  // TODO: should handle existing users
+  // TODO: should throw InvalidParameterException when a non-email is supplied as the Username when the pool has email as a UsernameAttribute
   // TODO: should send a message unless MessageAction=="SUPPRESS"
   // TODO: support MessageAction=="RESEND"
   // TODO: should generate a TemporaryPassword if one isn't set