package macaroons import ( "encoding/hex" "fmt" "google.golang.org/grpc/metadata" "golang.org/x/net/context" "gopkg.in/macaroon-bakery.v2/bakery" macaroon "gopkg.in/macaroon.v2" ) // MacaroonCredential wraps a macaroon to implement the // credentials.PerRPCCredentials interface. type MacaroonCredential struct { *macaroon.Macaroon } // RequireTransportSecurity implements the PerRPCCredentials interface. func (m MacaroonCredential) RequireTransportSecurity() bool { return true } // GetRequestMetadata implements the PerRPCCredentials interface. This method // is required in order to pass the wrapped macaroon into the gRPC context. // With this, the macaroon will be available within the request handling scope // of the ultimate gRPC server implementation. func (m MacaroonCredential) GetRequestMetadata(ctx context.Context, uri ...string) (map[string]string, error) { macBytes, err := m.MarshalBinary() if err != nil { return nil, err } md := make(map[string]string) md["macaroon"] = hex.EncodeToString(macBytes) return md, nil } // NewMacaroonCredential returns a copy of the passed macaroon wrapped in a // MacaroonCredential struct which implements PerRPCCredentials. func NewMacaroonCredential(m *macaroon.Macaroon) MacaroonCredential { ms := MacaroonCredential{} ms.Macaroon = m.Clone() return ms } // ValidateMacaroon validates the capabilities of a given request given a // bakery service, context, and uri. Within the passed context.Context, we // expect a macaroon to be encoded as request metadata using the key // "macaroon". func ValidateMacaroon(ctx context.Context, requiredPermissions []bakery.Op, svc *bakery.Bakery) error { // Get macaroon bytes from context and unmarshal into macaroon. md, ok := metadata.FromIncomingContext(ctx) if !ok { return fmt.Errorf("unable to get metadata from context") } if len(md["macaroon"]) != 1 { return fmt.Errorf("expected 1 macaroon, got %d", len(md["macaroon"])) } // With the macaroon obtained, we'll now decode the hex-string // encoding, then unmarshal it from binary into its concrete struct // representation. macBytes, err := hex.DecodeString(md["macaroon"][0]) if err != nil { return err } mac := &macaroon.Macaroon{} err = mac.UnmarshalBinary(macBytes) if err != nil { return err } // Check the method being called against the permitted operation and // the expiration time and IP address and return the result. authChecker := svc.Checker.Auth(macaroon.Slice{mac}) _, err = authChecker.Allow(ctx, requiredPermissions...) return err }