1. Connect to Skype for Business Online using remote PowerShell as shown below


  2. Run the following command to enable modern authentication:
    Set-CsOAuthConfiguration -ClientAdalAuthOverride Allowed

  3. Verify that the change was successful by running the following:
    Get-CsOAuthConfiguration


    Note: to disable modern authentication, run command: Set-CsOAuthConfiguration -ClientAdalAuthOverride NoOverride