diff --git a/src/flask_httpauth.py b/src/flask_httpauth.py
index f33f6c8..eca596f 100644
--- a/src/flask_httpauth.py
+++ b/src/flask_httpauth.py
@@ -254,13 +254,20 @@ def authenticate(self, auth, stored_password):
 
 
 class HTTPDigestAuth(HTTPAuth):
-    def __init__(self, scheme=None, realm=None, use_ha1_pw=False, qop='auth'):
+    def __init__(self, scheme=None, realm=None, use_ha1_pw=False, qop='auth',
+                 algorithm='MD5'):
         super(HTTPDigestAuth, self).__init__(scheme or 'Digest', realm)
         self.use_ha1_pw = use_ha1_pw
         if isinstance(qop, str):
             self.qop = [v.strip() for v in qop.split(',')]
         else:
             self.qop = qop
+        if algorithm.lower() == 'md5':
+            self.algorithm = 'MD5'
+        elif algorithm.lower() == 'md5-sess':
+            self.algorithm = 'MD5-Sess'
+        else:
+            raise ValueError(f'Algorithm {algorithm} is not supported')
         self.random = SystemRandom()
         try:
             self.random.random()
@@ -331,9 +338,10 @@ def authenticate_header(self):
         nonce = self.get_nonce()
         opaque = self.get_opaque()
         if self.qop:
-            return '{0} realm="{1}",nonce="{2}",opaque="{3}",qop="{4}"'.format(
+            return ('{0} realm="{1}",nonce="{2}",opaque="{3}",algorithm="{4}"'
+                    ',qop="{5}"').format(
                 self.scheme, self.realm, nonce,
-                opaque, ','.join(self.qop))
+                opaque, self.algorithm, ','.join(self.qop))
         else:
             return '{0} realm="{1}",nonce="{2}",opaque="{3}"'.format(
                 self.scheme, self.realm, nonce,
@@ -355,6 +363,9 @@ def authenticate(self, auth, stored_password_or_ha1):
             a1 = auth.username + ":" + auth.realm + ":" + \
                 stored_password_or_ha1
             ha1 = md5(a1.encode('utf-8')).hexdigest()
+        if self.algorithm == 'MD5-Sess':
+            ha1 = md5((ha1 + ':' + auth.nonce + ':' + auth.cnonce).encode(
+                'utf-8')).hexdigest()
         a2 = request.method + ":" + auth.uri
         ha2 = md5(a2.encode('utf-8')).hexdigest()
         if auth.qop == 'auth':
diff --git a/tests/test_digest_get_password.py b/tests/test_digest_get_password.py
index 8f6b4bf..6a6491f 100644
--- a/tests/test_digest_get_password.py
+++ b/tests/test_digest_get_password.py
@@ -1,5 +1,6 @@
 import unittest
 import re
+import pytest
 from hashlib import md5 as basic_md5
 from flask import Flask
 from flask_httpauth import HTTPDigestAuth
@@ -46,13 +47,32 @@ def digest_auth_route():
         self.digest_auth = digest_auth
         self.client = app.test_client()
 
+    def test_constructor(self):
+        d = HTTPDigestAuth()
+        assert d.qop == ['auth']
+        assert d.algorithm == 'MD5'
+        d = HTTPDigestAuth(qop=None)
+        assert d.qop is None
+        d = HTTPDigestAuth(qop='auth')
+        assert d.qop == ['auth']
+        d = HTTPDigestAuth(qop=['foo', 'bar'])
+        assert d.qop == ['foo', 'bar']
+        d = HTTPDigestAuth(qop='foo,bar, baz')
+        assert d.qop == ['foo', 'bar', 'baz']
+        d = HTTPDigestAuth(algorithm='md5')
+        assert d.algorithm == 'MD5'
+        d = HTTPDigestAuth(algorithm='md5-sess')
+        assert d.algorithm == 'MD5-Sess'
+        with pytest.raises(ValueError):
+            HTTPDigestAuth(algorithm='foo')
+
     def test_digest_auth_prompt(self):
         response = self.client.get('/digest')
         self.assertEqual(response.status_code, 401)
         self.assertTrue('WWW-Authenticate' in response.headers)
         self.assertTrue(re.match(r'^Digest realm="Authentication Required",'
                                  r'nonce="[0-9a-f]+",opaque="[0-9a-f]+",'
-                                 r'qop="auth"$',
+                                 r'algorithm="MD5",qop="auth"$',
                                  response.headers['WWW-Authenticate']))
 
     def test_digest_auth_ignore_options(self):
@@ -85,6 +105,34 @@ def test_digest_auth_login_valid(self):
                                                        d['opaque'])})
         self.assertEqual(response.data, b'digest_auth:john')
 
+    def test_digest_auth_md5_sess_login_valid(self):
+        self.digest_auth.algorithm = 'MD5-Sess'
+
+        response = self.client.get('/digest')
+        self.assertTrue(response.status_code == 401)
+        header = response.headers.get('WWW-Authenticate')
+        auth_type, auth_info = header.split(None, 1)
+        d = parse_dict_header(auth_info)
+
+        a1 = 'john:' + d['realm'] + ':bye'
+        ha1 = md5(
+            md5(a1).hexdigest() + ':' + d['nonce'] + ':foobar').hexdigest()
+        a2 = 'GET:/digest'
+        ha2 = md5(a2).hexdigest()
+        a3 = ha1 + ':' + d['nonce'] + ':00000001:foobar:auth:' + ha2
+        auth_response = md5(a3).hexdigest()
+
+        response = self.client.get(
+            '/digest', headers={
+                'Authorization': 'Digest username="john",realm="{0}",'
+                                 'nonce="{1}",uri="/digest",qop=auth,'
+                                 'nc=00000001,cnonce="foobar",response="{2}",'
+                                 'opaque="{3}"'.format(d['realm'],
+                                                       d['nonce'],
+                                                       auth_response,
+                                                       d['opaque'])})
+        self.assertEqual(response.data, b'digest_auth:john')
+
     def test_digest_auth_login_bad_realm(self):
         response = self.client.get('/digest')
         self.assertTrue(response.status_code == 401)
@@ -112,7 +160,7 @@ def test_digest_auth_login_bad_realm(self):
         self.assertTrue('WWW-Authenticate' in response.headers)
         self.assertTrue(re.match(r'^Digest realm="Authentication Required",'
                                  r'nonce="[0-9a-f]+",opaque="[0-9a-f]+",'
-                                 r'qop="auth"$',
+                                 r'algorithm="MD5",qop="auth"$',
                                  response.headers['WWW-Authenticate']))
 
     def test_digest_auth_login_invalid2(self):
@@ -142,7 +190,7 @@ def test_digest_auth_login_invalid2(self):
         self.assertTrue('WWW-Authenticate' in response.headers)
         self.assertTrue(re.match(r'^Digest realm="Authentication Required",'
                                  r'nonce="[0-9a-f]+",opaque="[0-9a-f]+",'
-                                 r'qop="auth"$',
+                                 r'algorithm="MD5",qop="auth"$',
                                  response.headers['WWW-Authenticate']))
 
     def test_digest_generate_ha1(self):