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auth.go
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auth.go
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// Copyright (c) 2019 Cisco and/or its affiliates.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at:
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package grpc
import (
"context"
"encoding/base64"
"strings"
"google.golang.org/grpc/codes"
"google.golang.org/grpc/credentials"
"google.golang.org/grpc/metadata"
"google.golang.org/grpc/peer"
"google.golang.org/grpc/status"
)
// Authenticator exposes a function for authenticating requests.
type Authenticator struct {
Username string
Password string
Token string
}
// Authenticate checks that a token exists and is valid. It stores the user
// metadata in the returned context and removes the token from the context.
func (a Authenticator) Authenticate(ctx context.Context) (newCtx context.Context, err error) {
defer func() {
if err == nil {
// Store user metadata
userMD := &UserMetadata{
ID: a.Username,
}
newCtx = context.WithValue(newCtx, userMDKey{}, userMD)
}
}()
err = a.tryTLSAuth(ctx)
if err == nil {
return ctx, nil
}
newCtx, err = a.tryTokenAuth(ctx)
if err == nil {
return newCtx, nil
}
return a.tryBasicAuth(ctx)
}
func (a Authenticator) tryTLSAuth(ctx context.Context) error {
p, ok := peer.FromContext(ctx)
if !ok {
return status.Error(codes.Unauthenticated, "no peer found")
}
tlsAuth, ok := p.AuthInfo.(credentials.TLSInfo)
if !ok {
return status.Error(codes.Unauthenticated, "unexpected peer transport credentials")
}
if len(tlsAuth.State.VerifiedChains) == 0 || len(tlsAuth.State.VerifiedChains[0]) == 0 {
return status.Error(codes.Unauthenticated, "could not verify peer certificate")
}
if tlsAuth.State.VerifiedChains[0][0].Subject.CommonName != a.Username {
return status.Error(codes.Unauthenticated, "invalid subject common name")
}
return nil
}
func (a Authenticator) tryBasicAuth(ctx context.Context) (context.Context, error) {
auth, err := extractHeader(ctx, "authorization")
if err != nil {
return ctx, err
}
const prefix = "Basic "
if !strings.HasPrefix(auth, prefix) {
return ctx, status.Error(codes.Unauthenticated, `missing "Basic " prefix in "Authorization" header`)
}
c, err := base64.StdEncoding.DecodeString(auth[len(prefix):])
if err != nil {
return ctx, status.Error(codes.Unauthenticated, `invalid base64 in header`)
}
cs := string(c)
s := strings.IndexByte(cs, ':')
if s < 0 {
return ctx, status.Error(codes.Unauthenticated, `invalid basic auth format`)
}
user, password := cs[:s], cs[s+1:]
if user != a.Username || password != a.Password {
return ctx, status.Error(codes.Unauthenticated, "invalid user or password")
}
// Remove token from headers from here on
return purgeHeader(ctx, "authorization"), nil
}
func (a Authenticator) tryTokenAuth(ctx context.Context) (context.Context, error) {
auth, err := extractHeader(ctx, "authorization")
if err != nil {
return ctx, err
}
const prefix = "Bearer "
if !strings.HasPrefix(auth, prefix) {
return ctx, status.Error(codes.Unauthenticated, `missing "Bearer " prefix in "Authorization" header`)
}
if strings.TrimPrefix(auth, prefix) != a.Token {
return ctx, status.Error(codes.Unauthenticated, "invalid token")
}
// Remove token from headers from here on
return purgeHeader(ctx, "authorization"), nil
}
func extractHeader(ctx context.Context, header string) (string, error) {
md, ok := metadata.FromIncomingContext(ctx)
if !ok {
return "", status.Error(codes.Unauthenticated, "no headers in request")
}
authHeaders, ok := md[header]
if !ok {
return "", status.Error(codes.Unauthenticated, "no header in request")
}
if len(authHeaders) != 1 {
return "", status.Error(codes.Unauthenticated, "more than 1 header in request")
}
return authHeaders[0], nil
}
func purgeHeader(ctx context.Context, header string) context.Context {
md, _ := metadata.FromIncomingContext(ctx)
mdCopy := md.Copy()
mdCopy[header] = nil
return metadata.NewIncomingContext(ctx, mdCopy)
}
type userMDKey struct{}
// UserMetadata contains metadata about a user.
type UserMetadata struct {
ID string
}
// GetUserMetadata can be used to extract user metadata stored in a context.
func GetUserMetadata(ctx context.Context) (*UserMetadata, bool) {
userMD := ctx.Value(userMDKey{})
switch md := userMD.(type) {
case *UserMetadata:
return md, true
default:
return nil, false
}
}