(Go) HMRC OAuth2 Access Token

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Note: This example requires Chilkat v10.1.2 or greater.

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    // To further clarify, see OAuth 2.0 Authorization Flow

    oauth2 := chilkat.NewOAuth2()

    // This should be the port in the localhost callback URL for your app.
    // Important: Make sure the callback URI in your HMRC developer app 
    // is exactly "http://localhost:3017/".  Don't forget the ending "/" char.
    // The callback URL would look like "http://localhost:3017/" if the port number is 3017.

    // IMPORTANT: Don't forget to setup your HMRC application to use the Redirect URI "http://localhost:3017/" as shown
    // here: Configure Redirect URI for HMRC application
    oauth2.SetListenPort(3017)

    oauth2.SetAuthorizationEndpoint("https://test-api.service.hmrc.gov.uk/oauth/authorize")
    oauth2.SetTokenEndpoint("https://test-api.service.hmrc.gov.uk/oauth/token")

    // Replace with your actual client ID
    oauth2.SetClientId("HMRC-CLIENT-ID")

    // The scopes are documented in the HMRC reference documentation for each API.
    // This example gets a read/write access token for the HMRC MTD VAT API.
    oauth2.SetScope("read:vat write:vat")

    // Begin the OAuth2 Authorization code flow.  This returns a URL that should be loaded in a browser.
    url := oauth2.StartAuth()
    if oauth2.LastMethodSuccess() != true {
        fmt.Println(oauth2.LastErrorText())
        oauth2.DisposeOAuth2()
        return
    }

    // Launch the default browser on the system and navigate to the url.
    // The LaunchBrowser method was added in Chilkat v10.1.2.
    success := oauth2.LaunchBrowser(*url)
    if success == false {
        fmt.Println(oauth2.LastErrorText())
        oauth2.DisposeOAuth2()
        return
    }

    // Wait for the user to approve or deny authorization in the browser.
    numMsWaited := 0
    for (numMsWaited < 90000) && (oauth2.AuthFlowState() < 3) {
        oauth2.SleepMs(100)
        numMsWaited = numMsWaited + 100
    }

    // If the browser does not respond within the specified time, AuthFlowState will be:
    // 
    // 1: Waiting for Redirect – The OAuth2 background thread is waiting for the browser's redirect request.
    // 2: Waiting for Final Response – The thread is awaiting the final access token response.
    // In either case, cancel the background task initiated by StartAuth.

    if oauth2.AuthFlowState() < 3 {
        oauth2.Cancel()
        fmt.Println("No response from the browser!")
        oauth2.DisposeOAuth2()
        return
    }

    // Check AuthFlowState to determine if authorization was granted, denied, or failed:
    // 
    // 3: Success – OAuth2 flow completed, the background thread exited, and the successful response is in AccessTokenResponse.
    // 4: Access Denied – OAuth2 flow completed, the background thread exited, and the error response is in AccessTokenResponse.
    // 5: Failure – OAuth2 flow failed before completion, the background thread exited, and error details are in FailureInfo.

    if oauth2.AuthFlowState() == 5 {
        fmt.Println("OAuth2 failed to complete.")
        fmt.Println(oauth2.FailureInfo())
        oauth2.DisposeOAuth2()
        return
    }

    if oauth2.AuthFlowState() == 4 {
        fmt.Println("OAuth2 authorization was denied.")
        fmt.Println(oauth2.AccessTokenResponse())
        oauth2.DisposeOAuth2()
        return
    }

    if oauth2.AuthFlowState() != 3 {
        fmt.Println("Unexpected AuthFlowState:", oauth2.AuthFlowState())
        oauth2.DisposeOAuth2()
        return
    }

    fmt.Println("OAuth2 authorization granted!")
    fmt.Println("Access Token = ", oauth2.AccessToken())

    // Get the full JSON response:
    json := chilkat.NewJsonObject()
    json.Load(oauth2.AccessTokenResponse())
    json.SetEmitCompact(false)
    fmt.Println(*json.Emit())

    // The JSON response looks like this:

    // {
    //   "token_type": "Bearer",
    //   "scope": "user_impersonation",
    //   "expires_in": "3599",
    //   "ext_expires_in": "0",
    //   "expires_on": "1524783438",
    //   "not_before": "1524779538",
    //   "resource": "https://mydomain.api.crm.dynamics.com",
    //   "access_token": "...",
    //   "refresh_token": "...",
    //   "id_token": "..."
    // }

    // If an "expires_on" member does not exist, then add the JSON member by
    // getting the current system date/time and adding the "expires_in" seconds.
    // This way we'll know when the token expires.
    if json.HasMember("expires_on") != true {
        dtExpire := chilkat.NewCkDateTime()
        dtExpire.SetFromCurrentSystemTime()
        dtExpire.AddSeconds(*json.IntOf("expires_in"))
        json.AppendString("expires_on",*dtExpire.GetAsUnixTimeStr(false))
    }

    fmt.Println(*json.Emit())

    // Save the JSON to a file for future requests.
    fac := chilkat.NewFileAccess()
    fac.WriteEntireTextFile("qa_data/tokens/hmrc.json",*json.Emit(),"utf-8",false)

    oauth2.DisposeOAuth2()
    json.DisposeJsonObject()
    dtExpire.DisposeCkDateTime()
    fac.DisposeFileAccess()