package sources in vs code

add nuget.config file in root

contents:

 <configuration>
    <packageSources>
        <add key="NuGet official package source" value="https://api.nuget.org/v3/index.json" />
        <add key="[source name]" value="https://blbla.pkgs.visualstudio.com/_packaging/Core/nuget" />
    </packageSources>
    <packageSourceCredentials>
    <[source name]>
        <add key="Username" value="email account" />
        <add key="ClearTextPassword" value="password" />
    </[source name]>
    </packageSourceCredentials>
    <trustedSigners>
        <author name="microsoft">
            <certificate fingerprint="[fingerprint]" hashAlgorithm="SHA256" allowUntrustedRoot="false" />
        </author>
    </trustedSigners>
</configuration>

https://docs.microsoft.com/nl-nl/nuget/reference/nuget-config-file