Simplify signature handling

This change brings a new SignatureHandler where Presigned.
Requests without Payload are handled very early before even
going through the call.

This change simplifies Donut codebase to not have signature related
logic for all API's.

Simplification is still needed for Payload based signature eg. PUT/POST calls
, which are still part of the donut codebase, which will be done subsequently
after donut re-write.

server-api-generic-handlers.go

@@ -21,7 +21,6 @@ import (
 	"net/http"
 	"time"
 
-	"github.com/minio/minio/pkg/auth"
 	"github.com/rs/cors"
 )
 
@@ -99,47 +98,6 @@ func (h timeHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	h.handler.ServeHTTP(w, r)
 }
 
-// ValidateAuthHeaderHandler - validate auth header handler is wrapper handler used
-// for request validation with authorization header. Current authorization layer
-// supports S3's standard HMAC based signature request.
-func ValidateAuthHeaderHandler(h http.Handler) http.Handler {
-	return validateAuthHandler{h}
-}
-
-// validate auth header handler ServeHTTP() wrapper
-func (h validateAuthHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
-	accessKeyID, err := stripAccessKeyID(r.Header.Get("Authorization"))
-	switch err.ToGoError() {
-	case errInvalidRegion:
-		writeErrorResponse(w, r, AuthorizationHeaderMalformed, r.URL.Path)
-		return
-	case errAccessKeyIDInvalid:
-		writeErrorResponse(w, r, InvalidAccessKeyID, r.URL.Path)
-		return
-	case nil:
-		// load auth config
-		authConfig, err := auth.LoadConfig()
-		if err != nil {
-			writeErrorResponse(w, r, InternalError, r.URL.Path)
-			return
-		}
-		// Access key not found
-		for _, user := range authConfig.Users {
-			if user.AccessKeyID == accessKeyID {
-				h.handler.ServeHTTP(w, r)
-				return
-			}
-		}
-		writeErrorResponse(w, r, InvalidAccessKeyID, r.URL.Path)
-		return
-	// All other errors for now, serve them
-	default:
-		// control reaches here, we should just send the request up the stack - internally
-		// individual calls will validate themselves against un-authenticated requests
-		h.handler.ServeHTTP(w, r)
-	}
-}
-
 // CorsHandler handler for CORS (Cross Origin Resource Sharing)
 func CorsHandler(h http.Handler) http.Handler {
 	return cors.Default().Handler(h)