A MyGet service endpoint is defined in VSTS services with my username and access token as a password, as per the documentation.
Package restore works fine during the build, unfortunately when using the NuGet push task, no packages are pushed and the following information appears in the log file:
"C:\Program Files\dotnet\dotnet.exe" nuget push d:\a\1\a\MyPackage.1.2.3.nupkg --sourcehttps://www.myget.org/F/myfeed/api/v2/package --api-key RequiredApiKey
2017-12-25T13:32:19.8275867Z info : Pushing Evolita.MyPackage.1.2.3.nupkg to 'https://www.myget.org/F/myfeed/api/v2/package'...
2017-12-25T13:32:19.8823758Z info : PUT https://www.myget.org/F/myfeed/api/v2/package/
2017-12-25T13:32:20.5401058Z info : Forbiddenhttps://www.myget.org/F/myfeed/api/v2/package/ 657ms
2017-12-25T13:32:20.7479361Z error: Response status code does not indicate success: 403 (Forbidden).
No packages are pushed to MyGet.
Cause and solution
VSTS incorrectly does not correctly use the API key configured. Please reach out to Microsoft support to make them aware, and use the following workaround for this issue:
1) Make sure the feed you are using is in NuGet.config.
2) In VSTS, configure two service connections for the feed.
The first service connection should use basic authentication using your username and an access token, and have the full feed URL that is also in NuGet.config. For example https://www.myget.org/F/myfeed/api/v2 or https://www.myget.org/F/myfeed/api/v3/index.json.
The second service connection should use API key authentication and have either the V2 push endpoint as the URL (https://www.myget.org/F/myfeed/api/v2/package), or the V3 endpoint (https://www.myget.org/F/myfeed/api/v3/index.json).