auth, etcdserver: allow users to know their roles and permissions

Current UserGet() and RoleGet() RPCs require admin permission. It
means that users cannot know which roles they belong to and what
permissions the roles have. This commit change the semantics and now
users can know their roles and permissions.

auth/store.go

@@ -165,6 +165,9 @@ type AuthStore interface {
 
 	// WithRoot generates and installs a token that can be used as a root credential
 	WithRoot(ctx context.Context) context.Context
+
+	// HasRole checks that user has role
+	HasRole(user, role string) bool
 }
 
 type TokenProvider interface {
@@ -1097,3 +1100,23 @@ func (as *authStore) WithRoot(ctx context.Context) context.Context {
 	tokenMD := metadata.New(mdMap)
 	return metadata.NewContext(ctx, tokenMD)
 }
+
+func (as *authStore) HasRole(user, role string) bool {
+	tx := as.be.BatchTx()
+	tx.Lock()
+	defer tx.Unlock()
+
+	u := getUser(tx, user)
+	if u == nil {
+		plog.Warningf("tried to check user %s has role %s, but user %s doesn't exist", user, role, user)
+		return false
+	}
+
+	for _, r := range u.Roles {
+		if role == r {
+			return true
+		}
+	}
+
+	return false
+}

etcdserver/apply_auth.go

@@ -189,6 +189,28 @@ func (aa *authApplierV3) checkLeasePuts(leaseID lease.LeaseID) error {
 	return nil
 }
 
+func (aa *authApplierV3) UserGet(r *pb.AuthUserGetRequest) (*pb.AuthUserGetResponse, error) {
+	err := aa.as.IsAdminPermitted(&aa.authInfo)
+	if err != nil && r.Name != aa.authInfo.Username {
+		aa.authInfo.Username = ""
+		aa.authInfo.Revision = 0
+		return &pb.AuthUserGetResponse{}, err
+	}
+
+	return aa.applierV3.UserGet(r)
+}
+
+func (aa *authApplierV3) RoleGet(r *pb.AuthRoleGetRequest) (*pb.AuthRoleGetResponse, error) {
+	err := aa.as.IsAdminPermitted(&aa.authInfo)
+	if err != nil && !aa.as.HasRole(aa.authInfo.Username, r.Role) {
+		aa.authInfo.Username = ""
+		aa.authInfo.Revision = 0
+		return &pb.AuthRoleGetResponse{}, err
+	}
+
+	return aa.applierV3.RoleGet(r)
+}
+
 func needAdminPermission(r *pb.InternalRaftRequest) bool {
 	switch {
 	case r.AuthEnable != nil:
@@ -203,16 +225,12 @@ func needAdminPermission(r *pb.InternalRaftRequest) bool {
 		return true
 	case r.AuthUserGrantRole != nil:
 		return true
-	case r.AuthUserGet != nil:
-		return true
 	case r.AuthUserRevokeRole != nil:
 		return true
 	case r.AuthRoleAdd != nil:
 		return true
 	case r.AuthRoleGrantPermission != nil:
 		return true
-	case r.AuthRoleGet != nil:
-		return true
 	case r.AuthRoleRevokePermission != nil:
 		return true
 	case r.AuthRoleDelete != nil: