diff -U 3 -dHrN -- a/trytond/protocols/wrappers.py b/trytond/protocols/wrappers.py
--- a/trytond/protocols/wrappers.py	2019-08-11 19:34:43.000000000 +0200
+++ b/trytond/protocols/wrappers.py	2021-07-27 15:59:38.213817153 +0200
@@ -8,7 +8,6 @@
 
 from werkzeug.wrappers import Request as _Request, Response
 from werkzeug.utils import cached_property
-from werkzeug.http import wsgi_to_bytes, bytes_to_wsgi
 from werkzeug.datastructures import Authorization
 from werkzeug.exceptions import abort, HTTPException
 
@@ -84,7 +83,8 @@
 def parse_authorization_header(value):
     if not value:
         return
-    value = wsgi_to_bytes(value)
+    if not isinstance(value, bytes):
+        value = value.encode('latin1')    
     try:
         auth_type, auth_info = value.split(None, 1)
         auth_type = auth_type.lower()
@@ -98,9 +98,9 @@
         except Exception:
             return
         return Authorization('session', {
-                'username': bytes_to_wsgi(username),
+                'username': username.decode("latin1"),                
                 'userid': userid,
-                'session': bytes_to_wsgi(session),
+                'session': session.decode("latin1"),                
                 })
 
 
@@ -171,16 +171,17 @@
             pool = Pool()
             UserApplication = pool.get('res.user.application')
 
-            authorization = wsgi_to_bytes(request.headers['Authorization'])
+            authorization = request.headers['Authorization']            
             try:
                 auth_type, auth_info = authorization.split(None, 1)
                 auth_type = auth_type.lower()
             except ValueError:
                 abort(401)
-            if auth_type != b'bearer':
+            if auth_type != 'bearer':
                 abort(403)
 
-            application = UserApplication.check(bytes_to_wsgi(auth_info), name)
+            application = UserApplication.check(auth_info, name)
+            
             if not application:
                 abort(403)
             transaction = Transaction()