The DefaultHyperClient does not support http - Issue with metadata server authentication

[pseguin2011]

When using the InstanceMetadata authentication, the default hyper client only enforces https, and the call to the metadata server fails (returning the following error: Token retrieval failed with error: error trying to connect: Unsupported scheme http)

My current solution is to simply create a custom client as seen below:

    match yup_oauth2::ApplicationDefaultCredentialsAuthenticator::with_client(
        opts,
        hyper::Client::builder().build(
            hyper_rustls::HttpsConnectorBuilder::new()
                .with_native_roots()
                .https_or_http()
                .enable_http1()
                .enable_http2()
                .build(),
        ),
    )
    .await
    {
        yup_oauth2::authenticator::ApplicationDefaultCredentialsTypes::InstanceMetadata(
            auth_builder,
        ) => {
            Ok(auth_builder.build().unwrap())
        }
        yup_oauth2::authenticator::ApplicationDefaultCredentialsTypes::ServiceAccount(auth_builder) => {
            Ok(auth_builder.build().await.unwrap())
            }
    }

[dermesser]

We had a discussion about this some time ago, the argument in favor of the current state was that HTTPS should (obviously) be preferred and thus enforced. However, I definitely see the problem of this case.

I am commenting more on the PR