Optionally allow json middleware to not check the content-type

src/middleware/json.js

@@ -7,12 +7,12 @@ function _mime(req) {
   return str.split(';')[0];
 }
 
-exports = module.exports = function (options) {
+exports = module.exports = function (options, forceContentType = true) {
     const json = express.json(options);
 
     return function (req, res, next) {
         // enforce json body type. without this the json middleware will skip parsing and req.body might be undefined
-        if (_mime(req) !== 'application/json') return res.status(400).send('incorrect mime type. expecting application/json');
+        if (forceContentType && _mime(req) !== 'application/json') return res.status(400).send('incorrect mime type. expecting application/json');
         json(req, res, next);
     };
 };