(Excel) Google Sheets Refresh an Expired Access Token

Demonstrates how to refresh an expired access token. If a Google Sheets REST API call results in a 401 "unauthorized" response, then it is likely the access token expired. An application should be able to automatically refresh the access token with no user interaction and then re-try the request with the newly obtained access token.

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'  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 Google Sheets OAuth2 Access Token

Dim jsonToken As Chilkat.JsonObject
Set jsonToken = Chilkat.NewJsonObject

success = jsonToken.LoadFile("qa_data/tokens/googleSheets.json")
If (success <> True) Then
    Debug.Print "Failed to load googleSheets.json"
    Exit Sub
End If

'  The access token JSON looks like this:

'  	{
'  	 "access_token": "abac.Ci-ZabcdF37-NUrmSzxbHxTsMbtlN-uPfabcdAQN_2ekzj0s5ofCzRabcdTDMGaa2Q",
'  	 "token_type": "Bearer",
'  	 "expires_in": 3600,
'  	 "refresh_token": "1/lEe5abcdNJ77eOSDBabcdkQGVmDalkwabcdR2Hatbo"
'  	}
' 

Dim oauth2 As Chilkat.OAuth2
Set oauth2 = Chilkat.NewOAuth2

oauth2.TokenEndpoint = "https://www.googleapis.com/oauth2/v4/token"

'  Replace these with actual values.
oauth2.ClientId = "GOOGLE-CLIENT-ID"
oauth2.ClientSecret = "GOOGLE-CLIENT-SECRET"

'  Get the "refresh_token"
oauth2.RefreshToken = jsonToken.StringOf("refresh_token")

'  Send the HTTP POST to refresh the access token..
success = oauth2.RefreshAccessToken()
If (success <> True) Then
    Debug.Print oauth2.LastErrorText
    Exit Sub
End If

'  The response contains a new access token, but we must keep
'  our existing refresh token for when we need to refresh again in the future.
success = jsonToken.UpdateString("access_token",oauth2.AccessToken)

'  Save the new JSON access token response to a file.
Dim sbJson As Chilkat.StringBuilder
Set sbJson = Chilkat.NewStringBuilder
jsonToken.EmitCompact = False
success = jsonToken.EmitSb(sbJson)
success = sbJson.WriteFile("qa_data/tokens/googleSheets.json","utf-8",False)

Debug.Print "OAuth2 authorization granted!"
Debug.Print "New Access Token = "; oauth2.AccessToken