perf: quick way to validate token string (#302)

parser.go

@@ -130,9 +130,6 @@ func (p *Parser) ParseUnverified(tokenString string, claims Claims) (token *Toke
 	// parse Header
 	var headerBytes []byte
 	if headerBytes, err = p.DecodeSegment(parts[0]); err != nil {
-		if strings.HasPrefix(strings.ToLower(tokenString), "bearer ") {
-			return token, parts, newError("tokenstring should not contain 'bearer '", ErrTokenMalformed)
-		}
 		return token, parts, newError("could not base64 decode header", ErrTokenMalformed, err)
 	}
 	if err = json.Unmarshal(headerBytes, &token.Header); err != nil {

request/extractor.go

@@ -90,7 +90,7 @@ func (e BearerExtractor) ExtractToken(req *http.Request) (string, error) {
 	tokenHeader := req.Header.Get("Authorization")
 	// The usual convention is for "Bearer" to be title-cased. However, there's no
 	// strict rule around this, and it's best to follow the robustness principle here.
-	if tokenHeader == "" || !strings.HasPrefix(strings.ToLower(tokenHeader), "bearer ") {
+	if len(tokenHeader) < 7 || !strings.HasPrefix(strings.ToLower(tokenHeader[:7]), "bearer ") {
 		return "", ErrNoTokenInRequest
 	}
 	return tokenHeader[7:], nil