Nuget.config file

In Azure DevOps' Package Feed, the user bustroker.packages.restore@bustroker.onmicrosoft.com needs to be added explicitly as a Reader, in the Feed’s Security tab. Then generate a Read Package PAT for that user.

//nuget.config
<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <packageSources>
    <clear />
    <add key="BustrokerPackages" value="https://pkgs.dev.azure.com/bustroker/_packaging/Bustroker.Packages./nuget/v3/index.json" />
  </packageSources>
  <packageSourceCredentials>
    <BustrokerPackages>
        <add key="Username" value="bustroker.packages.restore@bustroker.onmicrosoft.com" />
        <!-- Azure DevOps PAT that can ONLY ReadPackages -->
        <add key="ClearTextPassword" value="CLEAR_PAT" />
    </BustrokerPackages>
</packageSourceCredentials>
</configuration>

Environment Variables can be used as well

//nuget.config
  <packageSourceCredentials>
    <BustrokerPackages>
      <add key="Username" value="%USER_VARIABLE%" />      
      <add key="ClearTextPassword" value="%PAT%" />
    </BustrokerPackages>
  </packageSourceCredentials>

And encrypted password

//nuget.config
  <packageSourceCredentials>
    <BustrokerPackages>
      <add key="Username" value="bustroker.packages.restore@bustroker.onmicrosoft.com" />      
      <add key="Password" value="ENCRYPTED_PAT" />
    </BustrokerPackages>
  </packageSourceCredentials>

To encrypt the password, check here.