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

src/core/plugins/auth/actions.js

@@ -74,28 +74,23 @@ export const authorizePassword = ( auth ) => ( { authActions } ) => {
   let { schema, name, username, password, passwordType, clientId, clientSecret } = auth
   let form = {
     grant_type: "password",
-    scope: auth.scopes.join(scopeSeparator)
+    scope: auth.scopes.join(scopeSeparator),
+    username,
+    password
   }
   let query = {}
   let headers = {}
 
-  if ( passwordType === "basic") {
-    headers.Authorization = "Basic " + btoa(username + ":" + password)
-  } else {
-    Object.assign(form, {username}, {password})
+  switch (passwordType) {
+    case "request-body":
+      setClientIdAndSecret(form, clientId, clientSecret)
+      break
 
-    switch ( passwordType ) {
-      case "query":
-        setClientIdAndSecret(query, clientId, clientSecret)
-        break
-
-      case "request-body":
-        setClientIdAndSecret(form, clientId, clientSecret)
-        break
-
-      default:
-        headers.Authorization = "Basic " + btoa(clientId + ":" + clientSecret)
-    }
+    case "basic":
+      headers.Authorization = "Basic " + btoa(clientId + ":" + clientSecret)
+      break
+    default:
+      console.warn(`Warning: invalid passwordType ${passwordType} was passed, not including client id and secret`)
   }
 
   return authActions.authorizeRequest({ body: buildFormData(form), url: schema.get("tokenUrl"), name, headers, query, auth})