Nuget restore fails on Azure Devops with message "unable to load the service index for source"

Question

I have a build for a .NET solution that is running in a private agent. The solution contains both .NET Core 2.1 and .NET Standard 2.0 projects.

Some of the nuget packages installed are the following:

• NETStandard.Library v2.0.3
• Microsoft.AspNetCore.Mvc v2.0.0
• Microsoft.NETCore.App v2.1.5

The build fails when trying to restore the nuget packages with the following error:

"F:\Agent01\w\141\s\xxxxxxx.sln" (Restore target) (1) -> (Restore target) -> C:\Program Files\dotnet\sdk\2.1.500\NuGet.targets(114,5): error : Unable to load the service index for source https://xxxxxxxxxx.pkgs.visualstudio.com/_packaging/xxxxxxxxxx/nuget/v3/index.json. C:\Program Files\dotnet\sdk\2.1.500\NuGet.targets(114,5): error : Response status code does not indicate success: 401 (Unauthorized).

Build task is the following:

This is the content of %appdata%\NuGet\nuget.config file in the build agent:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <packageSources>
    <add key="nuget.org" value="https://api.nuget.org/v3/index.json" />
    <add key="MyFeed" value="https://xxxxxxxxxx.pkgs.visualstudio.com/_packaging/xxxxxxxxxx/nuget/v3/index.json" />
  </packageSources>
  <packageSourceCredentials>
    <MyFeed>
      <add key="Username" value="LocalBuildAgent" />
      <add key="ClearTextPassword" value="xxxxxxxxxxx" />
    </MyFeed>
  </packageSourceCredentials>
</configuration>

I already checked a few similar questions but so far I wasn't able to find a solution for my problem.

Some notes:

• Personal Access Token is NOT expired
• This particular build runs successfully in other build agents
• There is at least 1 build with a "nuget restore" task that was run successfully using this agent (regular nuget restore task, NOT .NET Core)
• Tried restarting the build agent, without success
• Tried specifying a specific version of nuget before the restore, without success
• .NET Core SDK latest version in the build agent is 2.1.500 (multiple versions installed)

What am I missing? How to fix this issue? Why can't I restore the packages using the dotnet restore command?

UPDATE:

Packages are restored without errors when using the old Nuget Restore task as follows:

UPDATE 2:

I am able to restore the packages using the .NET Core task v1:

Or using v2 task with argument --force:

Answer 1

I found a solution - add the following package source to %appdata%\NuGet\nuget.config:

<add key="Microsoft Visual Studio Offline Packages" value="C:\Program Files (x86)\Microsoft SDKs\NuGetPackages\" />

Complete file looks like this:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <packageSources>
    <add key="Microsoft Visual Studio Offline Packages" value="C:\Program Files (x86)\Microsoft SDKs\NuGetPackages\" />
    <add key="nuget.org" value="https://api.nuget.org/v3/index.json" />
    <add key="MyFeed" value="https://xxxxxxxxxx.pkgs.visualstudio.com/_packaging/xxxxxxxxxx/nuget/v3/index.json" />
  </packageSources>
  <packageSourceCredentials>
    <MyFeed>
      <add key="Username" value="LocalBuildAgent" />
      <add key="ClearTextPassword" value="xxxxxxxxxxx" />
    </MyFeed>
  </packageSourceCredentials>
</configuration>

Also, check Regression in .NET SDK 500: 'dotnet tool install' fails with 401 (Unauthorized) when there is a private feed in NuGet.config #7524. This problem seems to be caused by .NET SDK 2.1.500.

Another workaround would be to uninstall that version:

The issue is not present in .NET Core SDK 2.1.400, e.g. it goes away when .NET Core SDK 2.1.500 is uninstalled, and reappears when SDK 2.1.500 is installed again.