Scenario – You are trying to assign a work item to your colleague but unable to assign as it shows an error – “Sign-in required” as you type the username.

Solution -  Suppose you have tried clearing cache and logging in again to Azure DevOps portal and this doesn’t solve the issue, make sure the user who is trying to assign the work item has been given the right set of permissions in Azure Active Directory in which he is a member.

This user needs to have “Read Directory Data” permission in AAD so that he is able to read the user information and assign the work item.

Inside the AAD, search for the user and go to his details page. Click “Assigned roles” under “Manage” and check if he has already been assigned “Directory Readers” permission.  Users in this role can read basic directory information. 

If not assigned, ask the Azure Portal Administrator to assign the role for this user. Now, logout of the Azure DevOps portal and sign-in. You should now be able to assign the work items to your team members without any issues.