continue-flask-migratiion (#485)

Summary:

- Migrate auth mock collection to `flask`.
- Conform `Content-Type` for `aws` `JSON` with reality.
- Full cpmpliment of `robot` tests contiinue to succeed.

Author: general-kroll-4-life

test/mockserver/expectations/static-auth-testing-expectations.json

@@ -187,7 +187,7 @@ def match_route(self, req: Request) -> dict:
                     "template": "template_71.json",
                     "status": 200,
                     "response_headers": {
-                        "Content-Type": ["application/json"]
+                        "Content-Type": ["application/x-amz-json-1.0"]
                     }
                 }
             else: