ParseKey converts the binary contents of a private key file to an *rsa.PrivateKey.

RegisterBrokenAuthHeaderProvider previously did something.

HTTPClient is the context key to use with golang.org/x/net/context's WithValue function to associate an *http.Client value with a context.

AuthStyleCache is the set of tokenURLs we've successfully used via RetrieveToken and which style auth we ended up using.

ContextKey is just an empty struct.

LazyAuthStyleCache is a backwards compatibility compromise to let Configs have a lazily-initialized AuthStyleCache.

mirrors oauth2.RetrieveError.

Token represents the credentials used to authorize the requests to access protected resources on the OAuth 2.0 provider's backend.

AuthStyle is a copy of the golang.org/x/oauth2 package's AuthStyle type.