Move //mojo/services/X/public/... to //mojo/services/X/... (part 4).

mojo/services/vanadium/security/public/interfaces/principal.mojom

-// Copyright 2015 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-module vanadium;
-
-// Represents the name of an application. |url| is the url of the
-// application. |qualifier| is a string that allows to tie a specific
-// instance of an application to another.
-struct AppInstanceName {
-  string url;
-  string? qualifier;
-};
-
-// Certificate represents a human-readable name and public-key (DER encoded) pair.
-// The private-key for a certificate is only available for signing operations
-// within the principal service application.
-struct Certificate {
-   string extension;
-   array<uint8>? publickey;
-};
-
-// Blessing is a credential binding a user identity to a public key. The corresponding
-// private key is only available for signing within the PrincipalService application.
-struct Blessing {
-   array<Certificate> chain;
-};
-
-// ChainSeparator is the separator used to join name extensions in a certificate chain.
-const string ChainSeparator = "/";
-
-// A service that binds user identities to an application instance running in Mojo
-interface PrincipalService {
-  // Login is called by an application instance (requestor_url/qualifier) that
-  // wants to get a user blessing. The service may obtain the user blessing
-  // through a third-party authentication flow (eg:oauth2). The user blessing
-  // is bound to a public/private key-pair that this service generates and
-  // persists for this application instance. Returns null if login fails.
-  Login() => (Blessing? user_blessing);
-
-  // Removes the user blessing for the application instance that invokes the
-  // Logout method.
-  Logout();
-
-  // GetUserBlessing returns the user blessing for a given application instance.
-  // It returns an error if the application instance has not invoked Login().
-  GetUserBlessing(AppInstanceName app) => (Blessing? user_blessing);
-};
-