B4J Tutorial [BANano] Authentication to a B4J server (REST API)

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Included in the download of BANano is an example on how to connect with a Jetty B4J server. The example shows how you could use the B4J server to login/logoff and run a basic REST API call.

Together, they make a very powerful solution!

Note: because it needs a Cookie, you must run it on a server. You can quickly set one up with the "Web Browser For Chrome' plugin. Tutorial: https://www.b4x.com/android/forum/threads/banano-tip-running-a-test-server.100180
The example lets you login with a username (UserName) and password (Password). When correct (case sensitive), it returns an encrypted token that is then saved as a cookie on the browser side. For all the rest of the calls, this token is then used.

The relevant server code:
B4X:
'Filter class
Sub Class_Globals
   Dim NumberOfDays As Int = 90
End Sub

Public Sub Initialize
 
End Sub

'Return True to allow the request to proceed.
Public Sub Filter(req As ServletRequest, resp As ServletResponse) As Boolean
   Dim auths As List = req.GetHeaders("Authorization")
   Dim success As Boolean = False
   resp.SetHeader("Access-Control-Allow-Origin","*")
   resp.SetHeader("Access-Control-Allow-Methods" ,"GET, POST, OPTIONS")
   resp.SetHeader("Access-Control-Allow-Headers", "Access-Control-Allow-Headers, Origin, Accept, X-Requested-With, Content-Type, Access-Control-Request-Method, Access-Control-Request-Headers, Authorization")
   If auths.Size > 0 Then
       Dim auth As String = auths.Get(0)
       If auth.StartsWith("BANBasic") = True Then
           Dim b64 As String = auth.SubString("BANBasic ".Length)
           Dim su As StringUtils
           Dim b() As Byte = su.DecodeBase64(b64)
           Dim raw As String = BytesToString(b, 0, b.Length, "utf8")
           Dim UsernameAndPassword() As String = Regex.Split(":", raw)
           If CheckUsernameAndPassword(UsernameAndPassword) Then
               resp.Write($"{"BANanoStatus": 801, "BANToken": "${EncryptText(UsernameAndPassword(0) & ":" & UsernameAndPassword(1), "MyTopSecretPassword")}", "BANExpires": ${NumberOfDays}}"$)
               Return False            
           End If
       End If
       If auth.StartsWith("BANBearer") = True Then
           Dim b64 As String = auth.SubString("BANBearer ".Length)
           Dim dec As String = DecryptText(b64, "MyTopSecretPassword")
           Dim UsernameAndPassword() As String = Regex.Split(":", dec)
           success = CheckUsernameAndPassword(UsernameAndPassword)    
       End If
   End If
   If success = False Then
       ' we need to login
       resp.Write($"{"BANanoStatus": 800}"$)    
   End If
   Return success
End Sub

Sub CheckUsernameAndPassword(UsernameAndPassword() As String) As Boolean
   If UsernameAndPassword.Length = 2 Then
       'up to you to decide which credentials are allowed <---------------------------
       If UsernameAndPassword(0) = "UserName" And UsernameAndPassword(1) = "Password" Then
           Return True
       End If
   End If
   Return False
End Sub

' some helper functions
Sub EncryptText(text As String, password As String) As String
   Try
       Dim Su As StringUtils
       Dim c As B4XCipher
       Dim Crypt() As Byte = c.Encrypt(text.GetBytes("utf8"), password)
       Return Su.EncodeBase64(Crypt)
   Catch
       Return ""
   End Try
End Sub

Sub DecryptText(text As String, password As String) As String
   Try
       Dim Su As StringUtils
       Dim c As B4XCipher
       Dim BtCrypt() As Byte  = Su.DecodeBase64(text)
       Dim b() As Byte = c.Decrypt(BtCrypt, password)
       Return BytesToString(b, 0, b.Length, "utf8")
   Catch
       Return ""
   End Try
End Sub
The relevant Client code, which is transpiled to Javascript:
B4X:
public Sub BANano_Ready()
   Dim rows As List = MiniCSS.AddRows("r", 3, "row")
   MiniCSS.AddColumns("c",rows.get(0),2, "col-sm-6")
   MiniCSS.AddColumns("c",rows.get(1),1, "col-sm-12")
   MiniCSS.AddColumns("c",rows.get(2),1, "col-sm-12")
   MiniCSS.BuildGrid("body", rows)
 
   ' show a login or logoff button, depends if we have the Cookie
   Dim Token As String = BANano.GetCookie("BANanoDemoCookie")
   If Token = "" Then
       MiniCSS.Button("r1c1", "login", "Login", "primary", Me, False)
   Else
       MiniCSS.Button("r1c1", "login", "Log off", "primary", Me, False)
   End If
   MiniCSS.LoginForm("r1c1", "loginForm", Me)
 
   ' button to test our REST Api
   MiniCSS.Button("r2c1", "info", "Get Info", "", Me, False)
End Sub

public Sub Login_Clicked(event As BANanoEvent)
   Dim Token As String = BANano.GetCookie("BANanoDemoCookie")
   If Token = "" Then
       If BANano.CheckInternetConnectionWait Then
           ' open the popup
           BANano.GetElement("#loginform").SetChecked(True)
       Else
           ' no use to try to login
           MiniCSS.Content("r3c1", "contajax", "You are not connected to the internet!")
       End If
   Else
       BANano.RemoveCookie("BANanoDemoCookie", "")
       ' set to a log on button
       MiniCSS.Button("r1c1", "login", "Login", "primary", Me, True)
       MiniCSS.Content("r3c1", "contajax", "You are now logged off from the server!")
   End If
End Sub

public Sub Info_Clicked(event As BANanoEvent)
   If BANano.CheckInternetConnectionWait Then
       Dim Token As String = BANano.GetCookie("BANanoDemoCookie")
       If Token = "" Then
           ' we will have to login
           MiniCSS.Content("r3c1", "contajax", "You are not logged in on the server!")
           Return
       End If
       ' we are logged in, so lets get some REST api running
       Dim headers As Map
       headers.Initialize
       headers.put("Content-Type", "application/json")
       headers.Put("Authorization", $"BANBearer ${Token}"$)
       Dim res As String = BANano.CallAjaxWait("http://localhost:51042/getinfo","POST","json", "", False, headers)
       MiniCSS.Content("r3c1", "contajax", res)
   Else
       MiniCSS.Content("r3c1", "contajax", "You are not connected to the internet!")
   End If
End Sub

public Sub LoginformBtnLogin_Clicked(event As BANanoEvent)
   ' get the username and password
   Dim User As String = BANano.GetElement("#loginformusername").GetValue
   Dim Password As String = BANano.GetElement("#loginformpassword").GetValue
 
   ' close the popup
   BANano.GetElement("#loginform").SetChecked(False)
 
   ' try to logon to our server
   Dim headers As Map
   headers.Initialize
   headers.put("Content-Type", "application/json")
   headers.Put("Authorization", "BANBasic " & BANano.ToBase64(User & ":" & Password))
   Dim res As String = BANano.CallAjaxWait("http://localhost:51042/","POST","json", $""$, False, headers)
   Dim json As BANanoJSONParser
   json.Initialize(res)
   Dim m As Map = json.NextObject
   Dim CheckStatus As Int = m.GetDefault("BANanoStatus",0)
   Select Case CheckStatus
       Case 801 ' login is ok
           MiniCSS.Content("r3c1", "contajax", "You are logged in on the server!")
           Dim expires As Int = m.GetDefault("BANExpires", 0)
           BANano.SetCookie("BANanoDemoCookie", m.GetDefault("BANToken", ""), $"{"expires": ${expires}}"$)
           ' set to a logoff button
           MiniCSS.Button("r1c1", "login", "Log off", "primary", Me, True)
       Case Else ' login is not ok
           MiniCSS.Content("r3c1", "contajax", "You are not logged in on the server (wrong password?)!")
   End Select
End Sub
The communication to your jServer is done by doing Ajax calls e.g:
B4X:
Dim res As String = BANano.CallAjaxWait("http://localhost:51042/getinfo","POST","json", "", False, headers)
MiniCSS.Content("r3c1", "contajax", res)
What is ExternalTestConnectionServer?
By default the connection to the internet is tested by checking if donotdelete.gif can be retrieved
from the assets folder where the app is hosted.

However, if you do not put it on a host (e.g. just by opening the .html file from disk),
You can upload the donotdelete.gif to some host on the internet to test for an internet connection.
So in my case the gif is uploaded to http://gorgeousapps.com j(ust to test if the user has an internet connection). For production apps, you must put the gif to your own server, as I can not guarantee http://gorgeousapps.com will keep running forever.

A couple of interesting new commands in BANano to make this work:
B4X:
BANano.ToBase64 ' to send the username and password
.GetValue/.SetValue ' Umbrella had no methods for this, so I build them in
.GetChecked/.SetChecked ' Umbrella had no methods for this, so I build them in
BANano.Msgbox ' shows an alert
Steps to test the demo:
1. Run the Client code to generate the app
2. Start the Chrome Webserver plugin and point to the folder where client.html is
3. Start the B4J server
4. Browse to the Chrome Webserver (e.g. http://127.0.0.1:8887/client.html)
5. Click on Get Info -> note that you are not logged in
6. Click on Login, enter wrong username/password -> note that it is wrong
7. Click on Login, enter correct username/password: UserName/Password
8. Click on Get Info -> you get a hallo JSON
9. Click on logout
10. Click on Get Info -> note that you are not logged in

You can see the cookie in Application - Cookies.

Alain
 
Last edited:
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