Principal Service: Add support for multiple user accounts

services/vanadium/security/conventions.go

+// 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.
+
+package main
+
+import (
+        "fmt"
+        "strings"
+
+        vpkg "mojo/services/vanadium/security/interfaces/principal"
+)
+
+const chainSeparator = "/"
+
+// TODO(ataly): This is a hack! We should implement the security.BlessingNames
+// function from the Vanadium API.
+func name(chain []certificate) string {
+        if len(chain) == 0 {
+                return ""
+        }
+        name := chain[0].Extension
+        for i := 1; i < len(chain); i++ {
+                name = name + chainSeparator + chain[i].Extension
+        }
+        return name
+}
+
+// userFromBlessing returns a vpkg.User object constructed from a user
+// blessing chain in 'b', or nil if no such blessing chain exists.
+func userFromBlessings(b *wireBlessings) (vpkg.User, error) {
+        var (
+                rejected []string
+                empty    vpkg.User
+        )
+        for _, chain := range b.CertificateChains {
+                n := name(chain)
+                // n is valid OAuth2 token based blessing name iff
+                // n is of the form "dev.v.io/u/<clientID>/<email>"
+                parts := strings.Split(n, chainSeparator)
+                if len(parts) != 4 {
+                        rejected = append(rejected, n)
+                        continue
+                }
+                if (parts[0] != "dev.v.io") || (parts[1] != "u") {
+                        rejected = append(rejected, n)
+                        continue
+                }
+                // We assume that parts[2] must be the OAuth2 ClientID of
+                // this service, and parts[3] must be the user's email.
+                return vpkg.User{Email: parts[3]}, nil
+        }
+        return empty, fmt.Errorf("the set of blessings (%v) obtained from the Vanadium identity provider does not contain any user blessing chain", rejected)
+}