Understanding of sysprocesses

Question

I’m using the table sys.sysprocesses in the SQL 2012/2014, to identify through the field CONTEXT_INFO, which user of a particular application is tied to a particular session.

I created a function by passing as parameter the SPID.

CREATE FUNCTION [dbo].[FC_RETORNAUSUARIO] (@spid INTEGER)  
RETURNS sysname  
WITH EXECUTE AS CALLER  
AS  
BEGIN  

DECLARE @username sysname;

SET @username = suser_sname() DECLARE @contextinfo varbinary(128)
SELECT @contextinfo = context_info
FROM master.dbo.sysprocesses
WHERE spid = @spid DECLARE @offset int DECLARE @usernamelength int
  SET @usernamelength = substring(@contextinfo, datalength(@contextinfo), 1)
  SET @offset = datalength(@contextinfo) - @usernamelength - sign(@usernamelength) IF @usernamelength <> 0x00
  SET @username = convert(sysname, substring(@contextinfo, @offset, @usernamelength))
  SET @offset = @offset - 1 RETURN @username;

END;  

From this, I did a test with the application installed locally and together the instance used to connect and it worked. I got him to pass the application user.

But when putting on a server, I realized that the information from CONTEXT_INFO came empty. And that the user of the database in which the application was connected had no integration with Windows, IE, was a user created only for access to the bank.

The fact that the user does not have integration with Windows (not from the server domain) is what makes the context_info is not completed?