auth: add server interceptor

auth/server_interceptor.go

@@ -0,0 +1,58 @@
+package auth
+
+import (
+	"bytes"
+	"context"
+	"net/http"
+
+	"github.com/lightninglabs/loop/lsat"
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/metadata"
+)
+
+// ServerInterceptor is a gRPC server interceptor that extracts the token ID
+// from the request context if an LSAT is present.
+type ServerInterceptor struct{}
+
+// UnaryInterceptor is an unary gRPC server interceptor that inspects incoming
+// calls for authentication tokens. If an LSAT authentication token is found in
+// the request, its token ID is extracted and treated as client ID. The
+// extracted ID is then attached to the request context in a format that is easy
+// to extract by request handlers.
+func (i *ServerInterceptor) UnaryInterceptor(ctx context.Context,
+	req interface{}, _ *grpc.UnaryServerInfo, handler grpc.UnaryHandler) (
+	resp interface{}, err error) {
+
+	// Try getting the authentication header embedded in the context meta
+	// data and parse it. We ignore all errors that happen and just forward
+	// the request to the handler if anything fails. Incoming calls with
+	// invalid metadata will therefore just be treated as non-identified or
+	// non-authenticated.
+	md, ok := metadata.FromIncomingContext(ctx)
+	if !ok {
+		return handler(ctx, req)
+	}
+	header := &http.Header{
+		HeaderAuthorization: md.Get(HeaderAuthorization),
+	}
+	log.Debugf("Auth header present in request: %s",
+		md.Get(HeaderAuthorization))
+	macaroon, _, err := FromHeader(header)
+	if err != nil {
+		return handler(ctx, req)
+	}
+
+	// If there is an LSAT, decode and add it to the context.
+	identifier, err := lsat.DecodeIdentifier(bytes.NewBuffer(macaroon.Id()))
+	if err != nil {
+		return handler(ctx, req)
+	}
+	var clientID lsat.TokenID
+	copy(clientID[:], identifier.TokenID[:])
+	idCtx := AddToContext(ctx, KeyTokenID, clientID)
+	log.Debugf("Decoded client/token ID %s from auth header",
+		clientID.String())
+
+	// Continue the call chain by invoking the handler.
+	return handler(idCtx, req)
+}