Extend LUCI_CONTEXT["local_auth"] protocol to understand accounts.

common/auth/localauth/rpcs/getoauthtoken.go

Index: common/auth/localauth/rpcs/getoauthtoken.go
diff --git a/common/auth/localauth/rpcs/getoauthtoken.go b/common/auth/localauth/rpcs/getoauthtoken.go
index 7ba42d28cbc8af032e41bc538da5a45a5a7d4860..2605b4ac8407f7617a0b17f8e1b4661237615f87 100644
--- a/common/auth/localauth/rpcs/getoauthtoken.go
+++ b/common/auth/localauth/rpcs/getoauthtoken.go
@@ -10,18 +10,23 @@ import (
 
 // GetOAuthTokenRequest is parameters for GetOAuthToken RPC call.
 type GetOAuthTokenRequest struct {
-	Scopes []string `json:"scopes"`
-	Secret []byte   `json:"secret"`
+	Scopes    []string `json:"scopes"`
+	Secret    []byte   `json:"secret"`
+	AccountID string   `json:"account_id"`
 }
 
-// Validate checks that scopes and secret are set.
+// Validate checks that the request is structurally valid.
 func (r *GetOAuthTokenRequest) Validate() error {
 	switch {
 	case len(r.Scopes) == 0:
-		return fmt.Errorf(`Field "scopes" is required.`)
+		return fmt.Errorf(`field "scopes" is required`)

[iannucci, 2017/06/19 20:31:28]

may want to use errors.New so we get a stacktrace from here.

[Vadim Sh., 2017/06/19 20:41:36]

Done, though I don't really see a point in doing that.

 	case len(r.Secret) == 0:
-		return fmt.Errorf(`Field "secret" is required.`)
+		return fmt.Errorf(`field "secret" is required`)
 	}
+	// TODO(vadimsh): Uncomment when all old auth server are turned off.
+	//case r.AccountID == "":
+	//	return fmt.Errorf(`field "account_id" is required`)
+	//}
 	return nil
 }