(Lianja) Refresh GMail OAuth2 Access Token

Demonstrates how to refresh an expired or soon-to-expire GMail OAuth2 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 GMail OAuth2 Access Token

loJsonToken = createobject("CkJsonObject")
llSuccess = loJsonToken.LoadFile("qa_data/tokens/gmail.json")
if (llSuccess <> .T.) then
    ? "Failed to load googleSheets.json"
    release loJsonToken
    return
endif

// The access token JSON looks like this:

// 	{ 
// 	 "access_token": "abac.Ci-ZabcdF37-VUrmSzxbHxTsMbtlN-uPfabcdAQN_2ekzj0s5osCzRabcdTDMGaa2Q",
// 	 "token_type": "Bearer",
// 	 "expires_in": 3600,
// 	 "refresh_token": "1/lEe5abcdNJ77eOSDBabcdkQGVmDalkwabcdR2Hatbo"
// 	}
// 

loOauth2 = createobject("CkOAuth2")

loOauth2.TokenEndpoint = "https://www.googleapis.com/oauth2/v4/token"

// Replace these with actual values.
loOauth2.ClientId = "GOOGLE-CLIENT-ID"
loOauth2.ClientSecret = "GOOGLE-CLIENT-SECRET"

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

// Send the HTTP POST to refresh the access token..
llSuccess = loOauth2.RefreshAccessToken()
if (llSuccess <> .T.) then
    ? loOauth2.LastErrorText
    release loJsonToken
    release loOauth2
    return
endif

// 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.
loJsonToken.UpdateString("access_token",loOauth2.AccessToken)

// Save the new JSON access token response to a file.
loSbJson = createobject("CkStringBuilder")
loJsonToken.EmitCompact = .F.
loJsonToken.EmitSb(loSbJson)
loSbJson.WriteFile("qa_data/tokens/gmail.json","utf-8",.F.)

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


release loJsonToken
release loOauth2
release loSbJson