Hi Reguel,
I was able to add Authorization Basic  header before ApplicationSessionRequestFilter.
In result, the session of the user was changed based on this header.
However, the returned cookie form this request, is still not valid for the next calls ... ) the second call is authenticated as Developer)
I assume that this is a bug.
Here how you can reproduce it:
1. create project myapp with two REST endpoints (require authentication) (/ivy/api/myapp/loginCall and /ivy/api/myapp/checkCurrentUser); in both of them just log Ivy.session().getSessionUserName()
2. create user -> allan:allan
3. add this code snippet as index2.html and place it in \AxonIvyDesigner7.4.0\webapps\ivy
4. test it on http://localhost:8081/ivy/index2.html (clean cache/session first)
 <!DOCTYPE html> <html> <head> <meta
 charset="UTF-8"> html>
<html>
<head>
<meta charset="UTF-8">
<title>Test</title>
 <script
 <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.4.1/jquery.min.js"></script>
 <script>
 
 
	function loginCall() { {
	var authToken
 authToken = btoa('allan:allan'); //user and passowrd
   
 
    return $.ajax({
       url: "/ivy/api/myapp/loginCall",
       type: 'GET', 	  headers:{ 'GET',
	  headers:{
			'X-Requested-By': 'myapp',
 			'Content-Type':'application/json',
 			'Authorization': 'Basic ' +
 authToken + authToken
		},
       dataType: 'json'
     }); });
  }
    
  function checkProfile() {
   
 
    return $.ajax({
       url: "/ivy/api/myapp/checkCurrentUser",
       type: 'GET', 	  headers:{ 'GET',
	  headers:{
			'X-Requested-By': 'myapp',
 			'Content-Type':'application/json'
 		},
       dataType: 'json'
     }); });
  }
 
 
  $(document).ready(function() {
 	    	   
	  loginCall()
       .done(function() {
         checkProfile()
           .done(function(response) {
 			  
 			  
          }).fail(function() {
             
 
          });
       }).fail(function() {
        
 
      });
 	    
 	     });    </script> 	    
	  
  });
  
</script>
</head>
 
 <body> 
<body>
check F12 F12
</body>
 
 </html>
</html> 
 
 
BR, Yordan