Fixed panic issue

When verifying a token from a malformed Authorization header, values
without a space would cause a panic. Thanks to
https://www.reddit.com/user/gohacker for pointing out this problem!

jwt.go

@@ -107,7 +107,11 @@ func (m *Middleware) Secure(h http.Handler, v VerifyClaimsFunc) http.Handler {
 				return &jwtError{status: http.StatusUnauthorized, err: ErrMissingToken}
 			}
 		} else {
-			token = strings.Split(authHeader, " ")[1]
+			token_parts := strings.Split(authHeader, " ")
+			if len(token_parts) != 2 {
+				return &jwtError{status: http.StatusUnauthorized, err: ErrMalformedToken}
+			}
+			token = token_parts[1]
 		}
 
 		if status, err, message := m.VerifyToken(token, v, r); err != nil {

jwt_test.go

@@ -232,3 +232,16 @@ func TestGenerateTokenHandlerNotPOST(t *testing.T) {
 		t.Errorf("wanted %q, got %q", ErrInvalidMethod.Error(), body)
 	}
 }
+
+func TestMalformedAuthorizationHeader(t *testing.T) {
+	_, middleware := newToken(t)
+	token := "hello!"
+	resp := httptest.NewRecorder()
+	req, _ := http.NewRequest("GET", "http://example.com", nil)
+	req.Header.Set("Authorization", token) // No "Bearer " portion of header
+	middleware.Secure(testHandler, verifyClaimsFunc).ServeHTTP(resp, req)
+	body := strings.TrimSpace(resp.Body.String())
+	if body != ErrMalformedToken.Error() {
+		t.Errorf("wanted %q, got %q", ErrMalformedToken.Error(), body)
+	}
+}