Ignore case of auth scheme in request header

Some clients send an authorization header containing the "bearer"
keyword in lower case. This led to echo responding with "missing or
malformed jwt".

Request.BasicAuth (net/http) ignores the basic auth scheme's case since
a while: https://go-review.googlesource.com/c/go/+/111516/

middleware/jwt.go

@@ -295,7 +295,7 @@ func jwtFromHeader(header string, authScheme string) jwtExtractor {
 	return func(c echo.Context) (string, error) {
 		auth := c.Request().Header.Get(header)
 		l := len(authScheme)
-		if len(auth) > l+1 && auth[:l] == authScheme {
+		if len(auth) > l+1 && strings.EqualFold(auth[:l], authScheme) {
 			return auth[l+1:], nil
 		}
 		return "", ErrJWTMissing

middleware/jwt_test.go

@@ -261,6 +261,11 @@ func TestJWT(t *testing.T) {
 			expErrCode: http.StatusUnauthorized,
 			info:       "Token verification does not pass using a user-defined KeyFunc",
 		},
+		{
+			hdrAuth: strings.ToLower(DefaultJWTConfig.AuthScheme) + " " + token,
+			config:  JWTConfig{SigningKey: validKey},
+			info:    "Valid JWT with lower case AuthScheme",
+		},
 	} {
 		if tc.reqURL == "" {
 			tc.reqURL = "/"