improve: OAuth2 UI and test suite (via #5066)

* create `features` folder

* add base oauth2 server

* continue implementing OAuth tests

* WIP

* add password flow tests

* modify Password flow credential types

* remove query string credential type

* add test case for Authorization flow

* add specific Authorization value for Password flow test

* WIP

* fix linter issues

package.json

@@ -95,9 +95,11 @@
     "babel-preset-react": "^6.23.0",
     "babel-preset-stage-0": "^6.22.0",
     "babel-runtime": "^6.23.0",
+    "body-parser": "^1.18.3",
     "bundlesize": "^0.17.0",
     "chromedriver": "^2.38.3",
     "copy-webpack-plugin": "^4.0.1",
+    "cors": "^2.8.4",
     "css-loader": "^0.28.11",
     "cypress": "^3.1.0",
     "dedent": "^0.7.0",
@@ -108,6 +110,7 @@
     "eslint-plugin-mocha": "^4.11.0",
     "eslint-plugin-react": "^7.10.0",
     "expect": "^1.20.2",
+    "express": "^4.16.4",
     "extract-text-webpack-plugin": "^3.0.2",
     "file-loader": "^1.1.11",
     "git-describe": "^4.0.1",
@@ -124,6 +127,7 @@
     "npm-run-all": "^4.1.2",
     "null-loader": "0.1.1",
     "nyc": "^11.3.0",
+    "oauth2-server": "^2.4.1",
     "open": "0.0.5",
     "postcss-loader": "^2.1.5",
     "raw-loader": "0.5.1",