(Lianja) Refresh Expiring OAuth2 Access Token for Azure Registered App

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// We previously obtained an access token and saved the JSON to a file using this example:
// Get OAuth2 Access Token for Azure Registered App

// This example will examine the JSON and expiration date, and if near expiration will
// refresh the access token.

loJson = createobject("CkJsonObject")
llSuccess = loJson.LoadFile("qa_data/tokens/_myAzureApp.json")
if (llSuccess <> .T.) then
    ? "Failed to load the access token."
    release loJson
    return
endif

// The contents of the JSON look like this:
// {
//   "token_type": "Bearer",
//   "scope": "User.Read Mail.ReadWrite Mail.Send",
//   "expires_in": 3600,
//   "ext_expires_in": 0,
//   "access_token": "EwBAA8l6B...",
//   "refresh_token": "MCRMdbe6Cd...",
//   "id_token": "eyJ0eXAiOiJ...",
//   "expires_on": "1494112119"
// }

// The "expires_on" value is a Unix time.
loDtExpire = createobject("CkDateTime")
loDtExpire.SetFromUnixTime(.F.,loJson.IntOf("expires_on"))

// If this date/time expires within 10 minutes of the current system time, refresh the token.
if (loDtExpire.ExpiresWithin(10,"minutes") <> .T.) then
    ? "No need to refresh, the access token won't expire within the next 10 minutes."
    release loJson
    release loDtExpire
    return
endif

// OK, we need to refresh the access token..
loOauth2 = createobject("CkOAuth2")

// Note: The endpoint depends on the Azure App Registration.
// See How to Choose the Correct Endpoints for your Azure App Registration
loOauth2.TokenEndpoint = "https://login.microsoftonline.com/common/oauth2/v2.0/token"

// Use your client ID.
loOauth2.ClientId = "CLIENT_ID"

// Get the existing refresh token.
loOauth2.RefreshToken = loJson.StringOf("refresh_token")

// Send the HTTP POST to refresh the access token.
llSuccess = loOauth2.RefreshAccessToken()
if (llSuccess = .F.) then
    ? loOauth2.LastErrorText
    release loJson
    release loDtExpire
    release loOauth2
    return
endif

? "OAuth2 authorization granted!"
? "Access Token = " + loOauth2.AccessToken

// Get the full JSON response:
loJson.Load(loOauth2.AccessTokenResponse)
loJson.EmitCompact = .F.

// If an "expires_on" member does not exist, then add the JSON member by
// getting the current system date/time and adding the "expires_in" seconds.
// This way we'll know when the token expires.
if (loJson.HasMember("expires_on") <> .T.) then
    loDtExpire.SetFromCurrentSystemTime()
    loDtExpire.AddSeconds(loJson.IntOf("expires_in"))
    loJson.AppendString("expires_on",loDtExpire.GetAsUnixTimeStr(.F.))
endif

? loJson.Emit()

// Save the new access token JSON to a file for future requests.
loFac = createobject("CkFileAccess")
loFac.WriteEntireTextFile("qa_data/tokens/_myAzureApp.json",loJson.Emit(),"utf-8",.F.)


release loJson
release loDtExpire
release loOauth2
release loFac