Previously we just assumed support for the authorization code grant type,
but now we'll allow the host to declare which grant types it supports
to allow for more flexibility in host login implementations. We may extend
the set of supported grant types in future.
The OAuth specification requires several distinct arguments to be provided
to configure a client, rather than just a URL. To accommodate this, we'll
add a new method to the service discovery API to retrieve OAuth client
information in a Terraform-specific form. (The OAuth specification itself
considers this out of scope, because most OAuth clients are configured
by just hard-coding these settings into them for a particular remote
service.)
This PR improves the error handling so we can provide better feedback about any service discovery errors that occured.
Additionally it adds logic to test for specific versions when discovering a service using `service.vN`. This will enable more informational errors which can indicate any version incompatibilities.
This package implements our Terraform-native Service discovery protocol,
which allows us to find the base URL for a particular service given a
hostname that was already validated and normalized by the svchost package.
Martin Atkins