(Swift 2) Automatically Refresh Token for 401 Unauthorized

Demonstrates how to automatically refresh an access token (without user interaction) when the token expires and a 401 Unauthorized response is received.

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

    var tokenFilePath: String? = "qa_data/tokens/googleCalendar.json"

    // Get our current access token.
    let jsonToken = CkoJsonObject()
    var success: Bool = jsonToken.LoadFile(tokenFilePath)
    if jsonToken.HasMember("access_token") == false {
        print("No access token found.")
        return
    }

    let http = CkoHttp()
    http.AuthToken = jsonToken.StringOf("access_token")

    var jsonResponse: String? = http.QuickGetStr("https://www.googleapis.com/calendar/v3/users/me/calendarList")
    if http.LastMethodSuccess != true {

        if http.LastStatus.intValue != 401 {
            print("\(http.LastErrorText)")
            print("----")
            print("\(http.LastResponseBody)")
            return
        }

        // The access token must've expired. 
        // Refresh the access token and then retry the request.
        let oauth2 = CkoOAuth2()

        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 {
            print("\(oauth2.LastErrorText)")
            return
        }

        // 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.
        jsonToken.UpdateString("access_token", value: oauth2.AccessToken)

        // Save the new JSON access token response to a file.
        let sbJson = CkoStringBuilder()
        jsonToken.EmitCompact = false
        jsonToken.EmitSb(sbJson)
        sbJson.WriteFile(tokenFilePath, charset: "utf-8", emitBom: false)

        print("OAuth2 authorization granted!")
        print("New Access Token = \(oauth2.AccessToken)")

        // re-try the original request.
        http.AuthToken = oauth2.AccessToken
        jsonResponse = http.QuickGetStr("https://www.googleapis.com/calendar/v3/users/me/calendarList")
        if http.LastMethodSuccess != true {
            print("\(http.LastErrorText)")
            return
        }

    }

    print("\(jsonResponse!)")
    print("-----------------------------")

}