Salesforce OAuth2 Service is broken due to bad endpoint

[gmcinnes]

The Salesforce service looks up an OAuth2 endpoint at https://na1.salesforce.com/.......

Unfortunately, that endpoint no longer works. It's not clear if that's an intentional change on the part of Salesforce, but their documentation seems to suggest that the right endpoint at time of writing is https://login.salesforce.com/services/oauth2/token

See: https://developer.salesforce.com/docs/atlas.en-us.api_rest.meta/api_rest/intro_understanding_oauth_endpoints.htm