Allow slashes in authorize-session when using target name (#3249)

This requires specifying `**` as the selector in the proto, which will
match any segments and simply requires that the verb is the last part of
the URL, which it already is.

internal/proto/controller/api/services/v1/target_service.proto

@@ -75,9 +75,13 @@ service TargetService {
   }
 
   // AuthorizeSession creates authorization information from a given Target.
+  // Note that unlike most APIs, since we support using a target name along with
+  // scope ID or name to identify a target, this uses a pattern that allows the
+  // "id" field to have any number of segments, which works so long as the last
+  // part of the path is the verb, which is our normal pattern.
   rpc AuthorizeSession(AuthorizeSessionRequest) returns (AuthorizeSessionResponse) {
     option (google.api.http) = {
-      post: "/v1/targets/{id}:authorize-session"
+      post: "/v1/targets/{id=**}:authorize-session"
       body: "*"
       response_body: "item"
     };