Modifying the PowerBuilder client app

Purpose

In this section, we will modify the PowerBuilder application source code and the PowerServer project settings to achieve the following results:

  • Gets the user credential from the application login window, then authenticates it with the Amazon Cognito User Pools and gets an identity token.

  • Uses the identity token to access data from the PowerServer Web API.

  • Refreshes the identity token when necessary.

Add scripts

Step 1: Declare the following global variables.

//Token expiresin
Long gl_Expiresin
//Refresh token clockskew
Long gl_ClockSkew = 3

Step 2: Define a global function and name it f_Authorization().

Select from menu File > New; in the New dialog, select the PB Object tab and then select Function and click OK to add a global function.

This global function uses the HTTP Post method to send the user credentials to the authorization server and then gets the identity token from the HTTP Authorization header.

Add scripts to the f_Authorization() function to implement the following scenario: When the application starts, the application uses the username and password from the login window to get the token, and when the token expires, the login window displays for the user to input the username and password again.

The following scripts hard code the username and password instead of getting them from the login window. You can change the scripts to use the login window after you implement the login window and return the username and password to the f_Authorization() function.

//Integer f_Authorization() for password
//UserName & Password are passed from the login window
RestClient lrc_Client
String  ls_url, ls_UserName, ls_UserPass, ls_PostData, ls_Response, ls_expires_in
String  ls_TokenType, ls_AccessToken
String  ls_type, ls_description, ls_uri, ls_state
Integer li_Return, li_rtn
JsonParser ljson_Parser

li_rtn = -1
ls_url = profilestring("CloudSetting.ini","setup","TokenURL","")

//login window can be implemented to return username & password according to actual needs.
//Open(w_login) 
//Return UserName & Password

ls_UserName = "admin@test.com"
ls_UserPass = "appeon123"

If IsNull ( ls_UserName ) Or Len ( ls_UserName ) = 0 Then
 MessageBox( "Tips", "UserName is empty!" )
 Return li_rtn
End If
If IsNull ( ls_UserPass ) Or Len ( ls_UserPass ) = 0 Then
 MessageBox( "Tips", "Password is empty!" )
 Return li_rtn
End If

ls_PostData = '{"username":"' + ls_UserName + '", "password":"' + ls_UserPass + '"}';
lrc_Client = Create RestClient
lrc_Client.SetRequestHeader("Content-Type","application/json")
li_Return = lrc_Client.GetJWTToken( ls_Url, ls_PostData, ls_Response )
If li_Return = 1 and Pos ( ls_Response, "access_token" ) > 0 Then
 ljson_Parser = Create JsonParser
 ljson_Parser.LoadString(ls_Response)
 ls_TokenType = ljson_Parser.GetItemString("/token_type")
 ls_AccessToken = ljson_Parser.GetItemString("/access_token")
 //Application Set Authorization Header
 Getapplication().SetHttpRequesTheader("Authorization", ls_TokenType + " " +ls_AccessToken, true)
 //Set Global Variables
 gl_Expiresin = Long (ljson_Parser.GetItemNumber("/expires_in"))
 
 li_rtn = 1
Else
 MessageBox( "AccessToken Falied", "Return :" + String ( li_Return ) )
End If

If IsValid ( ljson_Parser ) Then DesTroy ( ljson_Parser )
If IsValid ( lrc_Client ) Then DesTroy ( lrc_Client )

Return li_rtn

Step 3: Insert a timing object (timing_1) to the application and add the following scripts to the Timer event of timing_1.

1) Open the application object and then select from menu Insert > Object > Timing to add a timing object to the application.

2) Add the following scripts to the Timer event of timing_1.

//Authenticates the user
f_Authorization()

When displayed in the source editor, the Timer event looks like this:

event timer;//Authenticates the user
f_Authorization()
end event


Step 4: Add the following scripts to the application Open event.

Place the scripts before the database connection is established. The scripts get the token from the built-in Cognito server and then start the user session (using the BeginSession function) to include the token information in the session.

//Authenticates the user and returns the token
If f_Authorization() <> 1 Then
 Return
End If

//Starts the session
long ll_return
Try
 ll_return = Beginsession()
 If ll_return <> 0 Then
  Messagebox("Beginsession Failed:" + String(ll_return), GetHttpResponseStatusText())
 End if
Catch ( Throwable ex)
 MessageBox( "Throwable", ex.GetMessage())
 Return
End Try

//Refreshes the token for timing
If gl_Expiresin > 0 And (gl_Expiresin - gl_ClockSkew) > 0 Then
 //Timer = Expiresin - ClockSkew 
 //7200 - 3
 timing_1.Start(gl_Expiresin - gl_ClockSkew)
End If

//Connects to db


Step 5: Add the following scripts to the SystemError event.

The scripts will trigger the SystemError event when the session or license encounters an error; and if the token is invalid or expires, the scripts will call the f_Authorization function to get the token again.

Choose Case error.Number
 Case 220  to 229 //Session Error
  MessageBox ("Session Error", "Number:" + String(error.Number) + "~r~nText:" + error.Text )
 Case 230  to 239 //License Error
  MessageBox ("License Error", "Number:" + String(error.Number) + "~r~nText:" + error.Text )
 Case 240  to 249 //Token Error
  MessageBox ("Token Error", "Number:" + String(error.Number) + "~r~nText:" + error.Text )
  //Authorization
  f_Authorization()
 Case Else
  MessageBox ("SystemError", "Number:" + String(error.Number) + "~r~nText:" + error.Text )
End Choose


Add an INI file

Create an INI file in the same location as the PBT file and name it CloudSetting.ini.

The INI file specifies the URL for requesting the token from the Amazon Cognito server. Notice that TokenURL points to the "/connect/token" API of the built-in Cognito server, and the Cognito server root URL (for example, http://localhost:5000/) is the same as the URL of PowerServer Web API. If you change the PowerServer Web API URL, change the root URL here accordingly.

[Setup]
TokenURL=http://localhost:5000/connect/token

Start session manually by code

By default, the user session is automatically created when the application starts; and the session includes no token. For the session to include the token, the session must be started manually by code instead of automatically.

To start the session manually by code,

Step 1: Enable "Begin session by code" in the PowerBuilder IDE. (Steps: Open the application object painter, click Additional Properties in the application's Properties dialog; in the Application dialog, select the PowerServer tab and then select the Begin session by code option.)

After this option is enabled, when the BeginSession function in the application Open event is called, it will create a session that includes the token information (See scripts in step 4 in "Add scripts").


Modify and re-deploy the PowerServer project

Step 1: Add the INI file CloudSetting.ini to the Files preloaded in uncompressed format section under the External Files tab.

Step 2: Select RESTClient Support and Compression Support under the Runtime tab.


Step 3: Double check the URL of the PowerServer Web APIs in the Web APIs tab. Make sure the port number is not occupied by any other program.

Tip: You can execute the command "netstat -ano | findstr portnumber" to check if the port number is occupied by any other program.

The built-in Cognito server will run at the same URL as the PowerServer Web API. If the PowerServer Web API URL is changed, change the root URL accordingly in the INI file.

Step 4: Double check that Use built-in AWS Cognito server is selected from the Auth Template list box in the Web APIs tab.

Step 5: Save the changes and deploy the PowerServer project (using the "Build & Deploy PowerServer Project" option) so that the above settings can take effect in the installable cloud app.