Restore nuget packages in msbuild 15 project - nuget

Question

I'd like to restore the nuget packages from a private feed (vsts internal feed) in a solution consisting of msbuild 15 projects, and subsequently build (and pack) the projects.
I'm using the VS 2017 hosted agent which I need to build.
I've tried restoring with msbuild with (the deprecated) package restore enabled. This results in no packages being restored. The relevant part of the logs:
2017-04-03T12:21:23.5543508Z ##[warning]The 'Restore NuGet Packages' option is deprecated. To restore NuGet packages in your build, add a NuGet Installer task to your build definition.
2017-04-03T12:21:23.5803410Z ##[command]"C:\LR\MMS\Services\mms\TaskAgentProvisioner\Tools\agents\2.115.0\externals\nuget\NuGet.exe" restore "C:\a\1\s\mysolution.sln" -NonInteractive
2017-04-03T12:21:24.5231560Z MSBuild auto-detection: using msbuild version '4.0' from 'C:\Windows\Microsoft.NET\Framework\v4.0.30319'.
I've tried restoring with the nuget installer task. This fails with
2017-04-03T12:21:05.3231625Z [command]C:\a_tasks\NuGetInstaller_333b11bd-d341-40d9-afcf-b32d5ce6f23b\0.2.29\node_modules\nuget-task-common\NuGet\3.5.0\NuGet.exe restore -NonInteractive C:\a\1\s\mysolution.sln -Verbosity Detailed -msbuildversion 15
2017-04-03T12:21:07.5100892Z NuGet Version: 3.5.0.1938
2017-04-03T12:21:07.8293660Z System.AggregateException: One or more errors occurred.
---> NuGet.CommandLine.CommandLineException: Failed to load msbuild Toolset
---> System.IO.FileNotFoundException: Could not load file or assembly 'Microsoft.Build, Version=14.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its dependencies. The system cannot find the file specified.
note that I pass in msbuildversion -15 as additional argument, but it seems nuget tries to load msbuild 14.
I've tried restoring with the dontnet cli dotnet restore. This fails with
2017-04-03T12:21:08.3424716Z [command]C:\Program Files\dotnet\dotnet.exe restore C:\a\1\s\path\to\my\csproj
2017-04-03T12:21:12.8146350Z Restoring packages for C:\a\1\s\path\to\my\csproj...
2017-04-03T12:21:12.8146350Z C:\Program Files\dotnet\sdk\1.0.0\NuGet.targets(97,5): error : Unable to load the service index for source https://myvstsaccount.pkgs.visualstudio.com/_packaging/Toolsfeed/nuget/v3/index.json. [C:\a\1\s\path\to\my\csproj]
2017-04-03T12:21:12.8146350Z C:\Program Files\dotnet\sdk\1.0.0\NuGet.targets(97,5): error : Response status code does not indicate success: 401 (Unauthorized). [C:\a\1\s\path\to\my\csproj]
2017-04-03T12:21:12.8176375Z ##[error]Dotnet command failed with non-zero exit code: 1.
The nuget.config in my solution directory is
<?xml version="1.0" encoding="utf-8"?>
<configuration>
<packageSources>
<add key="VSTS Tools Feed" value="https://myvstsaccount.pkgs.visualstudio.com/_packaging/Toolsfeed/nuget/v3/index.json" />
</packageSources>
<apikeys>
<add key="https://myvstsaccount.pkgs.visualstudio.com/_packaging/Toolsfeed/nuget/v3/index.json" value="<A PAT generated from an account with access to the feed>" />
</apikeys>
</configuration>
and the logs of the tasks show that the config is used.
Locally package restore works fine from VS, or with the nuget cli of nuget 4.0.
What task should I use to restore packages for msbuild 15 projects, and how can I configure authentication?

Answer 1

Restoring nuget packages defined as PackageReference elements in csproj project definitions requires nuget 4.0, which isn't included on the hosted build agents.
You can work around this restriction by including the nuget 4.0 binary in your source control tree, and referring to that binary within the package restore task as a custom NuGet version.
For example, when you include the nuget 4.0 binary in a file called nuget4.0.exe in the root directory of your source tree, you can specify the path as $(Build.SourcesDirectory)/nuget4.0.exe.
And there is a relate question here for you to refer.