(PureBasic) HMRC OAuth2 Access Token

Demonstrates how to get an HMRC OAuth2 access token from a desktop (installed) application or script. This example gets an HMRC MTD VAT read/write access token.

Chilkat PureBasic Module Download Chilkat PureBasic Module

IncludeFile "CkFileAccess.pb"
IncludeFile "CkHttp.pb"
IncludeFile "CkJsonObject.pb"
IncludeFile "CkOAuth2.pb"
IncludeFile "CkDateTime.pb"

Procedure ChilkatExample()

    ; This example requires the Chilkat API to have been previously unlocked.
    ; See Global Unlock Sample for sample code.

    oauth2.i = CkOAuth2::ckCreate()
    If oauth2.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    success.i

    ; 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
    CkOAuth2::setCkListenPort(oauth2, 3017)

    CkOAuth2::setCkAuthorizationEndpoint(oauth2, "https://test-api.service.hmrc.gov.uk/oauth/authorize")
    CkOAuth2::setCkTokenEndpoint(oauth2, "https://test-api.service.hmrc.gov.uk/oauth/token")

    ; Replace these with actual values.
    CkOAuth2::setCkClientId(oauth2, "HMRC-CLIENT-ID")
    CkOAuth2::setCkClientSecret(oauth2, "HMRC-CLIENT-SECRET")

    ; 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.
    CkOAuth2::setCkScope(oauth2, "read:vat write:vat")

    ; Begin the OAuth2 three-legged flow.  This returns a URL that should be loaded in a browser.
    url.s = CkOAuth2::ckStartAuth(oauth2)
    If CkOAuth2::ckLastMethodSuccess(oauth2) <> 1
        Debug CkOAuth2::ckLastErrorText(oauth2)
        CkOAuth2::ckDispose(oauth2)
        ProcedureReturn
    EndIf

    http.i = CkHttp::ckCreate()
    If http.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    ; At this point, your application should load the URL in a browser.
    ; For example, 
    ; in C#: System.Diagnostics.Process.Start(url);
    ; in Java: Desktop.getDesktop().browse(new URI(url));
    ; in VBScript: Set wsh=WScript.CreateObject("WScript.Shell")
    ;              wsh.Run url
    ; in Xojo: ShowURL(url)  (see http://docs.xojo.com/index.php/ShowURL)
    ; in Dataflex: Runprogram Background "c:\Program Files\Internet Explorer\iexplore.exe" sUrl        
    ; The GitHub account owner would interactively accept or deny the authorization request.

    ; Add the code to load the url in a web browser here...
    ; Add the code to load the url in a web browser here...
    ; Add the code to load the url in a web browser here...

    ; Now wait for the authorization.
    ; We'll wait for a max of 120 seconds.
    numMsWaited.i = 0
    While (numMsWaited < 120000) AND (CkOAuth2::ckAuthFlowState(oauth2) < 3)
        CkOAuth2::ckSleepMs(oauth2,100)
        numMsWaited = numMsWaited + 100
    Wend

    ; If there was no response from the browser within 30 seconds, then 
    ; the AuthFlowState will be equal to 1 or 2.
    ; 1: Waiting for Redirect. The OAuth2 background thread is waiting to receive the redirect HTTP request from the browser.
    ; 2: Waiting for Final Response. The OAuth2 background thread is waiting for the final access token response.
    ; In that case, cancel the background task started in the call to StartAuth.
    If CkOAuth2::ckAuthFlowState(oauth2) < 3
        CkOAuth2::ckCancel(oauth2)
        Debug "No response from the browser!"
        CkOAuth2::ckDispose(oauth2)
        CkHttp::ckDispose(http)
        ProcedureReturn
    EndIf

    ; Check the AuthFlowState to see if authorization was granted, denied, or if some error occurred
    ; The possible AuthFlowState values are:
    ; 3: Completed with Success. The OAuth2 flow has completed, the background thread exited, and the successful JSON response is available in AccessTokenResponse property.
    ; 4: Completed with Access Denied. The OAuth2 flow has completed, the background thread exited, and the error JSON is available in AccessTokenResponse property.
    ; 5: Failed Prior to Completion. The OAuth2 flow failed to complete, the background thread exited, and the error information is available in the FailureInfo property.
    If CkOAuth2::ckAuthFlowState(oauth2) = 5
        Debug "OAuth2 failed to complete."
        Debug CkOAuth2::ckFailureInfo(oauth2)
        CkOAuth2::ckDispose(oauth2)
        CkHttp::ckDispose(http)
        ProcedureReturn
    EndIf

    If CkOAuth2::ckAuthFlowState(oauth2) = 4
        Debug "OAuth2 authorization was denied."
        Debug CkOAuth2::ckAccessTokenResponse(oauth2)
        CkOAuth2::ckDispose(oauth2)
        CkHttp::ckDispose(http)
        ProcedureReturn
    EndIf

    If CkOAuth2::ckAuthFlowState(oauth2) <> 3
        Debug "Unexpected AuthFlowState:" + Str(CkOAuth2::ckAuthFlowState(oauth2))
        CkOAuth2::ckDispose(oauth2)
        CkHttp::ckDispose(http)
        ProcedureReturn
    EndIf

    Debug "OAuth2 authorization granted!"
    Debug "Access Token = " + CkOAuth2::ckAccessToken(oauth2)

    ; Get the full JSON response:
    json.i = CkJsonObject::ckCreate()
    If json.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    CkJsonObject::ckLoad(json,CkOAuth2::ckAccessTokenResponse(oauth2))
    CkJsonObject::setCkEmitCompact(json, 0)
    Debug CkJsonObject::ckEmit(json)

    ; 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 CkJsonObject::ckHasMember(json,"expires_on") <> 1
        dtExpire.i = CkDateTime::ckCreate()
        If dtExpire.i = 0
            Debug "Failed to create object."
            ProcedureReturn
        EndIf

        CkDateTime::ckSetFromCurrentSystemTime(dtExpire)
        CkDateTime::ckAddSeconds(dtExpire,CkJsonObject::ckIntOf(json,"expires_in"))
        CkJsonObject::ckAppendString(json,"expires_on",CkDateTime::ckGetAsUnixTimeStr(dtExpire,0))
    EndIf

    Debug CkJsonObject::ckEmit(json)

    ; Save the JSON to a file for future requests.
    fac.i = CkFileAccess::ckCreate()
    If fac.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    CkFileAccess::ckWriteEntireTextFile(fac,"qa_data/tokens/hmrc.json",CkJsonObject::ckEmit(json),"utf-8",0)


    CkOAuth2::ckDispose(oauth2)
    CkHttp::ckDispose(http)
    CkJsonObject::ckDispose(json)
    CkDateTime::ckDispose(dtExpire)
    CkFileAccess::ckDispose(fac)


    ProcedureReturn
EndProcedure