Interns/feature/ge app mode proxy endpoint

[omersayshi]

Overview

Just merging in the feature branch into interns/dev. All the commits into the feature branch has been reviewed so this should be a quick one.

Testing Instructions (the same testing instructions as PR#14)

NOTE: Alot of overhead is required to test this PR. to make it easier, ping me on Teams for a ClientId and ClientSecret to avoid registering an app and installing a Teams app on a test tenant with the same ClientId.

• Open the file appsettings.json
• In ClientId, paste the clientId of your app registration
• In ClientSecret, paste the client secret of your app registration
• Head over to Graph Explorer
• Go to Access token and copy the access token
• Run the branch locally and open Postman
• Add your access token that was copied from GE into the Authorization tab as a 'Bearer Token'
• Make a call to the API using the endpoint /graphproxy/{ADD YOUR GRAPH QUERY HERE}. Example: /v1.0/teams/{team-id}/channels
• Make sure its a Graph call on a Teams resource (Team or Chat) that you are a owner of and have the GE Teams app (with the same client Id as the you pasted in appsettings.json) installed on (in order for the Graph request to work)

Expected behavior

• If you have the teams app installed on the resource you are trying to call AND you are the owner of that resource, you will receive a 200 OK with the response
• If you have the teams app installed on the resource you are trying to call AND you are the NOT owner of that resource, you will receive a 403 forbidden with an empty response
• If you dont have the teams app installed on the resource you are trying to call, you will receive a 403 forbidden with an error message from Graph.

[acchiang]

touched base offline; lgtm