We missed this in the original interface specification, but the `grant_type=authorization_code` requires it, per RFC6749 (https://tools.ietf.org/html/rfc6749#section-4.1.3).
Signed-off-by: Matt Moyer <moyerm@vmware.com>
This allows the token exchange request to be performed with the correct TLS configuration.
We go to a bit of extra work to make sure the `http.Client` object is cached between reconcile operations so that connection pooling works as expected.
Signed-off-by: Matt Moyer <moyerm@vmware.com>
