macOS: GSSAPI operation failed on Nuget restore

28th October 2019

When restoring packages from a remote on-prem Nuget repository on macOS, you may run into either one of the following error messages:

GSSAPI operation failed with error - An unsupported mechanism was requested
Unable to load the service index for source https://tfs.partner.com/DefaultCollection/_packaging/Nuget/nuget/v3/index.json
As covered in [this old, but unresolved ticket](https://github.com/Microsoft/artifacts-credprovider/issues/45), the problem usually stems from incorrect auth handling when downgrading the mode of authentication (e.g from Kerberos to Basic).

To work around the issue you need to:

  1. generate a personal acess token (PAT) that gives you rights to the given service;

  2. configure your Nuget.config to use the PAT for authentication using Basic auth:

    <?xml version="1.0" encoding="utf-8"?>
<configuration>
    <packageSources>
        <add key="NuGet official package source" value="https://api.nuget.org/v3/index.json" />
        <add key="Partner" value="https://tfs.partner.com/DefaultCollection/_packaging/Nuget/nuget/v3/index.json" />
    </packageSources>
    <packageSourceCredentials>
        <Partner> 
            <add key="Username" value="USERNAME" />
            <add key="ClearTextPassword" value="PATSTRING" />
            <add key="ValidAuthenticationTypes" value="basic" /> 
        </Partner>
    </packageSourceCredentials>
</configuration>

  3. clear the cache and restore the packages using the old HTTP client:

    cd repo
nuget locals -clear all
export DOTNET_SYSTEM_NET_HTTP_USESOCKETSHTTPHANDLER=0
nuget restore