(VB.NET) OAuth2 Token using IdentityServer4 with Client Credentials

Demonstrates how to get an OAuth2 access token using the client credential flow with IdentityServer4.

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

Dim http As New Chilkat.Http

' The first step is to fetch your IdentityServer4's discovery document
' (OpenID Connect defines a discovery mechanism, called OpenID Connect Discovery, where an OpenID server publishes its metadata at a well-known URL, 
' typically https://server.com/.well-known/openid-configuration


Dim resp As Chilkat.HttpResponse = http.QuickRequest("GET","https://localhost:5000/.well-known/openid-configuration")
If (http.LastMethodSuccess <> True) Then
    Debug.WriteLine(http.LastErrorText)
    Exit Sub
End If


If (resp.StatusCode <> 200) Then
    Debug.WriteLine("Received response status code " & resp.StatusCode)
    Debug.WriteLine("Response body containing error text or JSON:")
    Debug.WriteLine(resp.BodyStr)

    Exit Sub
End If


Dim json As New Chilkat.JsonObject
Dim success As Boolean = json.Load(resp.BodyStr)


' We have the discovery document, which contains something like this:

' You can use this online tool to generate parsing code from sample JSON: 
' Generate Parsing Code from JSON

' {
'   "issuer": "https://localhost:5000",
'   "jwks_uri": "https://localhost:5000/.well-known/openid-configuration/jwks",
'   "authorization_endpoint": "https://localhost:5000/connect/authorize",
'   "token_endpoint": "https://localhost:5000/connect/token",
'   "userinfo_endpoint": "https://localhost:5000/connect/userinfo",
'   "end_session_endpoint": "https://localhost:5000/connect/endsession",
'   "check_session_iframe": "https://localhost:5000/connect/checksession",
'   "revocation_endpoint": "https://localhost:5000/connect/revocation",
'   "introspection_endpoint": "https://localhost:5000/connect/introspect",
'   "frontchannel_logout_supported": true,
'   "frontchannel_logout_session_supported": true,
'   "backchannel_logout_supported": true,
'   "backchannel_logout_session_supported": true,
'   "scopes_supported": [
'     "openid",
'     "profile",
'     "email",
'     "MyCompany.profile",
'     "MyCompany.Identity.WebApi",
'     "MyCompany.TriHub.WebApi",
'     "offline_access"
'   ],
'   "claims_supported": [
'     "sub",
'     "updated_at",
'     "locale",
'     "zoneinfo",
'     "birthdate",
'     "gender",
'     "website",
'     "profile",
'     "preferred_username",
'     "nickname",
'     "middle_name",
'     "given_name",
'     "family_name",
'     "name",
'     "picture",
'     "email_verified",
'     "email",
'     "userId",
'     "groups",
'     "fullname"
'   ],
'   "grant_types_supported": [
'     "authorization_code",
'     "client_credentials",
'     "refresh_token",
'     "implicit",
'     "password"
'   ],
'   "response_types_supported": [
'     "code",
'     "token",
'     "id_token",
'     "id_token token",
'     "code id_token",
'     "code token",
'     "code id_token token"
'   ],
'   "response_modes_supported": [
'     "form_post",
'     "query",
'     "fragment"
'   ],
'   "token_endpoint_auth_methods_supported": [
'     "client_secret_basic",
'     "client_secret_post"
'   ],
'   "subject_types_supported": [
'     "public"
'   ],
'   "id_token_signing_alg_values_supported": [
'     "RS256"
'   ],
'   "code_challenge_methods_supported": [
'     "plain",
'     "S256"
'   ]
' }
' 


' The next steps are to (1) get the token_endpoint,
' and (2) verify that the client_credentials grant type is supported.

Dim tokenEndpoint As String = json.StringOf("token_endpoint")

Dim grantTypes As Chilkat.JsonArray = json.ArrayOf("grant_types_supported")
Dim clientCredentialsIdx As Integer = grantTypes.FindString("client_credentials",True)


' If clientCredentialsIdx is less then zero (-1) then the "client_credentials" string was not found.
If (clientCredentialsIdx < 0) Then
    Debug.WriteLine("The client credentials grant type is not supported.")
    Exit Sub
End If


' Request the access token using our Client ID and Client Secret.
' We're going to duplicate this CURL statement:

' curl --request POST \
'   --url '<tokenEndpoint>' \
'   --header 'content-type: application/x-www-form-urlencoded' \
'   --data 'grant_type=client_credentials&client_id=CLIENT_ID&client_secret=CLIENT_SECRET'


Dim req As New Chilkat.HttpRequest
req.HttpVerb = "POST"
req.AddParam("grant_type","client_credentials")
req.AddParam("client_id","CLIENT_ID")
req.AddParam("client_secret","CLIENT_SECRET")

resp = http.PostUrlEncoded(tokenEndpoint,req)
If (http.LastMethodSuccess = False) Then
    Debug.WriteLine(http.LastErrorText)
    Exit Sub
End If


' Make sure we got a 200 response status code, otherwise it's an error.
If (resp.StatusCode <> 200) Then
    Debug.WriteLine("POST to token endpoint failed.")
    Debug.WriteLine("Received response status code " & resp.StatusCode)
    Debug.WriteLine("Response body containing error text or JSON:")
    Debug.WriteLine(resp.BodyStr)

    Exit Sub
End If


success = json.Load(resp.BodyStr)


' Our JSON response should contain this:
' {
'   "access_token":"eyJz93a...k4laUWw",
'   "token_type":"Bearer",
'   "expires_in":86400
' }

' Get the access token:
Dim accessToken As String = json.StringOf("access_token")

' The access token is what gets added to "Authorization: Bearer <access_token>"
' for the subsequent REST API calls..