(VB.NET UWP/WinRT) Using the OAuth2 Authorization Token in REST API Calls

Demonstrates how to use an OAuth2 authorization token in REST API calls after obtaining it.

Chilkat Universal Windows Platform (UWP) / WinRT Downloads Chilkat for the Universal Windows Platform (UWP)

' This example assumes the Chilkat API to have been previously unlocked.
' See Global Unlock Sample for sample code.

' This example demonstrates how to include the OAuth2 authorization token in HTTP requests (REST API calls).
' An OAuth2 authorization token is typically in JSON format, and looks something like this:

' {
'   "token_type": "Bearer",
'   "scope": "openid profile User.ReadWrite Mail.ReadWrite Mail.Send Files.ReadWrite User.Read Calendars.ReadWrite Group.ReadWrite.All",
'   "expires_in": 3600,
'   "ext_expires_in": 3600,
'   "access_token": "EwCQA8l6...rW5az09bI0C",
'   "refresh_token": "MCZhZ...6jBNRcpuQW",
'   "id_token": "eyJ0eXAi...kcuQQrT03jMyA",
'   "expires_on": "1569281808"
' }

' A few notes about the JSON above:
' 
' 1) Different OAuth2 implementations (servers) may have different JSON members. 
'    The important ones for this discussion are "access_token" and "refresh_token".   
'    These members should always be named exactly "access_token" and "refresh_token".  
'    (I've never seen them named differently, although I don't think it's a formal standard.)
' 
' 2) The "id_token" is present if you obtained the OAuth2 authorization token including "openid" in the scope.
'    It contains information about the user.  It is a JWT (per the OIDC specification) and here is the Chilkat
'    example for decoding the id_token.
' 
' 3) If you don't have a "refresh_token" in your JSON, some REST API's require "offline_access" to be included
'    in the scope when obtaining the OAuth2 token.
' 
' 4) IMPORTANT: Quite often, access_token's are only valid for a limited amount of time.  (Often just 1 hour (i.e. 3600 seconds)).
'    When the access token expires, your HTTP request will fail with a 401 Unauthorized status response.  This is where your application
'    can automatically recover by fetching a new access_token and re-sending the request.  I'll explain...  
'    Usually getting an OAuth2 token for a user requires interactive approval from the user in a browser.
'    However, refreshing the access_token does NOT require user interaction.  You should design
'    your application to automatically recover from an expired access token by 
'    (A) Automatically fetch a new access_token using the refresh_token as shown in this example.
'    (B) Persist the new JSON to wherever you're storing the access token, such as in a file or database record.  You'll need it for the next time you refresh.
'    (C) Update the http.AuthToken or rest.Authorization property (as shown below)
'    (D) Re-send the request using the updated auth token.
'    The above 4 steps (A, B, C, D) can be automatic such that the user never notices, except for a small delay in performance.

' When your application obtains the OAuth2 access token, it should store the JSON in persistent manner, such as in 
' a file, a database record, etc.  The "access_token" is used by your application when sending REST requests.  Typically, it is sent
' in the Authorization request header.  For example:
' 
' Authorization: Bearer <token>
' 

' -----
' Chilkat has two classes for sending HTTP requests.  One is named "Http" and the other is named "Rest".  Either can be used.  
' Once you become familiar with both, you'll find that some requests are more convenient to code in one or the other.
' 
' I'll demonstrate how to get the access_token from the JSON and add the Authorization header for both cases.
' 

' ----
' ---- (1) Get the access_token ----
Dim json As New Chilkat.JsonObject
Dim success As Boolean = json.LoadFile("qa_data/tokens/myToken.json")
If (success <> True) Then
    Debug.WriteLine(json.LastErrorText)
    Exit Sub
End If


' Get the access_token member.
Dim accessToken As String = json.StringOf("access_token")

' ----
' ---- (2) Demonstrate adding the "Authorization: Bearer <token>" header using Chilkat Http ----
Dim http As New Chilkat.Http

' Setting the AuthToken property causes the "Authorization: Bearer <token>" header to be added to each request.
http.AuthToken = accessToken

' For example:
Dim responseStr As String = Await http.QuickGetStrAsync("https://example.com/someApiCall")

' Another example:
Dim req As New Chilkat.HttpRequest
' ...
Dim resp As Chilkat.HttpResponse = Await http.PostUrlEncodedAsync("https://example.com/someApiCall",req)
' ...

' In both of the above cases, the "Authorization: Bearer <token>" header is automatically added to each request.

' ----
' ---- (3) Add the Authorization header using Chilkat Rest ----
Dim rest As New Chilkat.Rest

success = Await rest.ConnectAsync("example.com",443,True,True)
' ...

' Set the Authorization property to "Bearer <token>"
Dim sbAuthHeaderVal As New Chilkat.StringBuilder
sbAuthHeaderVal.Append("Bearer ")
sbAuthHeaderVal.Append(accessToken)
rest.Authorization = sbAuthHeaderVal.GetAsString()

' All requests sent by the rest object will now include the "Authorization: Bearer <token>" header.

' For example:
responseStr = Await rest.FullRequestNoBodyAsync("GET","/someApiCall")