(Visual FoxPro) Refresh a Constant Contact OAuth2 Access Token

Refreshes a Constant Contact OAuth2 access token. When an access token expires, HTTPS requests will receive a 401 status response indicating failure. When that happens, your application can run this code to refresh the access token, and then retry the request using the new access token. Refreshing an access token does not need user interaction (i.e. does not need to display a browser to have the user interactive authorize access).

For more information, see https://v3.developer.constantcontact.com/api_guide/server_flow.html#step-5-refresh-the-access-token

Chilkat ActiveX Downloads ActiveX for 32-bit and 64-bit Windows

LOCAL loJsonToken
LOCAL lnSuccess
LOCAL loOauth2
LOCAL loSbJson

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

* It is assumed we previously obtained an OAuth2 access token.
* This example loads the JSON access token file 
* saved by this example: Get Constant Contact OAuth2 Access Token

* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.JsonObject')
loJsonToken = CreateObject('Chilkat.JsonObject')
lnSuccess = loJsonToken.LoadFile("qa_data/tokens/constantContact.json")
IF (lnSuccess <> 1) THEN
    ? "Failed to load constantContact.json"
    RELEASE loJsonToken
    CANCEL
ENDIF

* The access token JSON looks like this:

* {
*   "access_token": "aEr4czHReESHUGcc2LRknzsMxUbW",
*   "refresh_token": "s2qH27ikM7r3Ia0LrZGDOIgKw0bubUotBdJ7fTtc7y",
*   "token_type": "Bearer"
* }

* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.OAuth2')
loOauth2 = CreateObject('Chilkat.OAuth2')

loOauth2.VerboseLogging = 1

loOauth2.TokenEndpoint = "https://idfed.constantcontact.com/as/token.oauth2"
loOauth2.UseBasicAuth = 1
loOauth2.UncommonOptions = "OAUTH2_REFRESH_NO_SCOPE"

* Replace these with actual values.
loOauth2.ClientId = "CLIENT_KEY"
loOauth2.ClientSecret = "CLIENT_SECRET"

* Get the "refresh_token"
loOauth2.RefreshToken = loJsonToken.StringOf("refresh_token")

? "Existing refresh_token: " + loOauth2.RefreshToken

* Send the HTTP POST to refresh the access token..
lnSuccess = loOauth2.RefreshAccessToken()
IF (lnSuccess <> 1) THEN
    ? loOauth2.LastErrorText
    RELEASE loJsonToken
    RELEASE loOauth2
    CANCEL
ENDIF

loJsonToken.UpdateString("access_token",loOauth2.AccessToken)
loJsonToken.UpdateString("refresh_token",loOauth2.RefreshToken)

* Save the new JSON access token response to a file.
* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.StringBuilder')
loSbJson = CreateObject('Chilkat.StringBuilder')
loJsonToken.EmitCompact = 0
loJsonToken.EmitSb(loSbJson)
loSbJson.WriteFile("qa_data/tokens/constantContact.json","utf-8",0)

? "OAuth2 token refreshed!"
? "New Access Token = " + loOauth2.AccessToken
? "New refresh_token: " + loOauth2.RefreshToken

RELEASE loJsonToken
RELEASE loOauth2
RELEASE loSbJson