(Lianja) 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..
loSbToken = createobject("CkStringBuilder")
llSuccess = loSbToken.LoadFile("qa_data/tokens/googleCloudStorageAccessToken.txt","utf-8")
if (llSuccess = .F.) then
    ? "Failed to load access token."
    release loSbToken
    return
endif

loHttp = createobject("CkHttp")

loHttp.AuthToken = loSbToken.GetAsString()

// Construct a URL to download an object named "starfish.jpg" from the "chilkat-ocean" bucket.
loHttp.SetUrlVar("bucket_name","chilkat-ocean")
loHttp.SetUrlVar("object_name","starfish.jpg")
lcUrl = "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..
loFileData = createobject("CkBinData")
llSuccess = loHttp.DownloadBd(lcUrl,loFileData)
lnResponseCode = loHttp.LastStatus
if ((llSuccess = .F.) and (lnResponseCode <> 401)) then
    ? loHttp.LastErrorText
    release loSbToken
    release loHttp
    release loFileData
    return
endif

if (lnResponseCode = 401) then
    ? "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.
    loFac = createobject("CkFileAccess")
    lcJsonKey = loFac.ReadEntireTextFile("qa_data/googleApi/ChilkatCloud-13a07a2e8b3f.json","utf-8")
    if (loFac.LastMethodSuccess <> .T.) then
        ? loFac.LastErrorText
        release loSbToken
        release loHttp
        release loFileData
        release loFac
        return
    endif

    loGAuth = createobject("CkAuthGoogle")
    loGAuth.JsonKey = lcJsonKey
    loGAuth.Scope = "https://www.googleapis.com/auth/cloud-platform"
    loGAuth.ExpireNumSeconds = 3600
    loGAuth.SubEmailAddress = ""

    loTlsSock = createobject("CkSocket")
    llSuccess = loTlsSock.Connect("www.googleapis.com",443,.T.,5000)
    if (llSuccess <> .T.) then
        ? loTlsSock.LastErrorText
        release loSbToken
        release loHttp
        release loFileData
        release loFac
        release loGAuth
        release loTlsSock
        return
    endif

    llSuccess = loGAuth.ObtainAccessToken(loTlsSock)
    if (llSuccess <> .T.) then
        ? loGAuth.LastErrorText
        release loSbToken
        release loHttp
        release loFileData
        release loFac
        release loGAuth
        release loTlsSock
        return
    endif

    loFac.WriteEntireTextFile("qa_data/tokens/googleCloudStorageAccessToken.txt",loGAuth.AccessToken,"utf-8",.F.)

    // Retry the original request.
    loHttp.AuthToken = loGAuth.AccessToken
    llSuccess = loHttp.DownloadBd(lcUrl,loFileData)
    if (llSuccess = .F.) then
        ? loHttp.LastErrorText
        release loSbToken
        release loHttp
        release loFileData
        release loFac
        release loGAuth
        release loTlsSock
        return
    endif

endif

if (lnResponseCode <> 200) then
    // Get the error response
    loSbErrorResponse = createobject("CkStringBuilder")
    loSbErrorResponse.AppendBd(loFileData,"utf-8",0,0)
    ? "Error response code = " + str(lnResponseCode)
    ? "Error:"
    ? loSbErrorResponse.GetAsString()
    release loSbToken
    release loHttp
    release loFileData
    release loFac
    release loGAuth
    release loTlsSock
    release loSbErrorResponse
    return
endif

? "Success."

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


release loSbToken
release loHttp
release loFileData
release loFac
release loGAuth
release loTlsSock
release loSbErrorResponse