(Excel) Refresh Access Token on 401 Unauthorized and Retry

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 Chilkat.StringBuilder
Set sbToken = Chilkat.NewStringBuilder

success = sbToken.LoadFile("qa_data/tokens/googleCloudStorageAccessToken.txt","utf-8")
If (success = False) Then
    Debug.Print "Failed to load access token."
    Exit Sub
End If

Dim http As Chilkat.Http
Set http = Chilkat.NewHttp

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")

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 Chilkat.BinData
Set fileData = Chilkat.NewBinData
success = http.DownloadBd(url,fileData)

responseCode = http.LastStatus
If ((success = False) And (responseCode <> 401)) Then
    Debug.Print http.LastErrorText
    Exit Sub
End If

If (responseCode = 401) Then
    Debug.Print "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 Chilkat.FileAccess
    Set fac = Chilkat.NewFileAccess

    jsonKey = fac.ReadEntireTextFile("qa_data/googleApi/ChilkatCloud-13a07a2e8b3f.json","utf-8")
    If (fac.LastMethodSuccess <> True) Then
        Debug.Print fac.LastErrorText
        Exit Sub
    End If

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

    Dim tlsSock As Chilkat.Socket
    Set tlsSock = Chilkat.NewSocket
    success = tlsSock.Connect("www.googleapis.com",443,True,5000)
    If (success <> True) Then
        Debug.Print tlsSock.LastErrorText
        Exit Sub
    End If

    success = gAuth.ObtainAccessToken(tlsSock)
    If (success <> True) Then
        Debug.Print gAuth.LastErrorText
        Exit Sub
    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
        Debug.Print http.LastErrorText
        Exit Sub
    End If

End If

If (responseCode <> 200) Then
    ' Get the error response
    Dim sbErrorResponse As Chilkat.StringBuilder
    Set sbErrorResponse = Chilkat.NewStringBuilder
    success = sbErrorResponse.AppendBd(fileData,"utf-8",0,0)
    Debug.Print "Error response code = "; responseCode
    Debug.Print "Error:"
    Debug.Print sbErrorResponse.GetAsString()
    Exit Sub
End If

Debug.Print "Success."

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