(Xojo Plugin) Refresh Access Token on 401 Unauthorized and Retry (Service Account)

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Demonstrates how to handle an expired access token error, refresh the token, and retry the request. (In this case, the request is to download an object from Google Cloud Storage.)

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

// This example uses a previously obtained access token having permission for the 
// scope "https://www.googleapis.com/auth/cloud-platform"

// In this example, Get Google Cloud Storage OAuth2 Access Token, 
// the service account access token was saved to a text file.  This example fetches the access token from the file..
Dim sbToken As New Chilkat.StringBuilder
Dim success As Boolean
success = sbToken.LoadFile("qa_data/tokens/googleCloudStorageAccessToken.txt","utf-8")
If (success = False) Then
    System.DebugLog("Failed to load access token.")
    Return
End If

Dim http As New Chilkat.Http

http.AuthToken = sbToken.GetAsString()

// Construct a URL to download an object named "starfish.jpg" from the "chilkat-ocean" bucket.
success = http.SetUrlVar("bucket_name","chilkat-ocean")
success = http.SetUrlVar("object_name","starfish.jpg")
Dim url As String
url = "https://www.googleapis.com/storage/v1/b/{$bucket_name}/o/{$object_name}?alt=media"

// If there is an error response, then we didn't actually download the file data,
// but instead we downloaded an error response..
Dim fileData As New Chilkat.BinData
success = http.DownloadBd(url,fileData)
Dim responseCode As Int32
responseCode = http.LastStatus
If ((success = False) And (responseCode <> 401)) Then
    System.DebugLog(http.LastErrorText)
    Return
End If

If (responseCode = 401) Then
    System.DebugLog("Received 401 Unauthorized response. Attempting to refresh the access token...")

    // May be that the access token expired.
    // Load our JSON key and request a new access token, then retry the original request.
    Dim fac As New Chilkat.FileAccess
    Dim jsonKey As String
    jsonKey = fac.ReadEntireTextFile("qa_data/googleApi/ChilkatCloud-13a07a2e8b3f.json","utf-8")
    If (fac.LastMethodSuccess <> True) Then
        System.DebugLog(fac.LastErrorText)
        Return
    End If

    Dim gAuth As New Chilkat.AuthGoogle
    gAuth.JsonKey = jsonKey
    gAuth.Scope = "https://www.googleapis.com/auth/cloud-platform"
    gAuth.ExpireNumSeconds = 3600
    gAuth.SubEmailAddress = ""

    Dim tlsSock As New Chilkat.Socket
    success = tlsSock.Connect("www.googleapis.com",443,True,5000)
    If (success <> True) Then
        System.DebugLog(tlsSock.LastErrorText)
        Return
    End If

    success = gAuth.ObtainAccessToken(tlsSock)
    If (success <> True) Then
        System.DebugLog(gAuth.LastErrorText)
        Return
    End If

    success = fac.WriteEntireTextFile("qa_data/tokens/googleCloudStorageAccessToken.txt",gAuth.AccessToken,"utf-8",False)

    // Retry the original request.
    http.AuthToken = gAuth.AccessToken
    success = http.DownloadBd(url,fileData)
    If (success = False) Then
        System.DebugLog(http.LastErrorText)
        Return
    End If

End If

If (responseCode <> 200) Then
    // Get the error response
    Dim sbErrorResponse As New Chilkat.StringBuilder
    success = sbErrorResponse.AppendBd(fileData,"utf-8",0,0)
    System.DebugLog("Error response code = " + Str(responseCode))
    System.DebugLog("Error:")
    System.DebugLog(sbErrorResponse.GetAsString())
    Return
End If

System.DebugLog("Success.")

// Save the downloaded data to a file.
success = fileData.WriteFile("qa_output/starfish.jpg")