Initial version of the proxy.

Missing: logging, an Authenticator implementing the LSAT HTTP
and gRPC protocol.

auth/interface.go

@@ -0,0 +1,15 @@
+package auth
+
+import "net/http"
+
+// Authenticator is the generic interface for validating client headers and
+// returning new challenge headers.
+type Authenticator interface {
+	// Accept returns whether or not the header successfully authenticates the user
+	// to a given backend service.
+	Accept(*http.Header) bool
+
+	// FreshChallengeHeader returns a header containing a challenge for the user to
+	// complete.
+	FreshChallengeHeader(r *http.Request) (http.Header, error)
+}