diff --git a/flask_authz/casbin_enforcer.py b/flask_authz/casbin_enforcer.py
index c807574..0386ca3 100644
--- a/flask_authz/casbin_enforcer.py
+++ b/flask_authz/casbin_enforcer.py
@@ -16,7 +16,7 @@ class CasbinEnforcer:
 
     e = None
 
-    def __init__(self, app, adapter, watcher=None):
+    def __init__(self, app=None, adapter=None, watcher=None):
         """
         Args:
             app (object): Flask App object to get Casbin Model
@@ -24,10 +24,18 @@ def __init__(self, app, adapter, watcher=None):
         """
         self.app = app
         self.adapter = adapter
-        self.e = casbin.Enforcer(app.config.get("CASBIN_MODEL"), self.adapter)
-        if watcher:
-            self.e.set_watcher(watcher)
+        self.e = None
+        self.watcher = watcher
         self._owner_loader = None
+        self.user_name_headers = None
+        if self.app is not None:
+            self.init_app(self.app)
+
+    def init_app(self, app):
+        self.app = app
+        self.e = casbin.Enforcer(app.config.get("CASBIN_MODEL"), self.adapter)
+        if self.watcher:
+            self.e.set_watcher(self.watcher)
         self.user_name_headers = app.config.get("CASBIN_USER_NAME_HEADERS", None)
 
     def set_watcher(self, watcher):
diff --git a/tests/test_casbin_enforcer_init_app.py b/tests/test_casbin_enforcer_init_app.py
new file mode 100644
index 0000000..321f2c9
--- /dev/null
+++ b/tests/test_casbin_enforcer_init_app.py
@@ -0,0 +1,207 @@
+import pytest
+from casbin.enforcer import Enforcer
+from flask import request, jsonify
+from casbin_sqlalchemy_adapter import Adapter
+from casbin_sqlalchemy_adapter import Base
+from casbin_sqlalchemy_adapter import CasbinRule
+from sqlalchemy import create_engine
+from sqlalchemy.orm import sessionmaker
+from flask_authz import CasbinEnforcer
+
+
+def enforcer_partial():
+    engine = create_engine("sqlite://")
+    adapter = Adapter(engine)
+
+    session = sessionmaker(bind=engine)
+    Base.metadata.create_all(engine)
+    s = session()
+    s.query(CasbinRule).delete()
+    s.add(CasbinRule(ptype="p", v0="alice", v1="/item", v2="GET"))
+    s.add(CasbinRule(ptype="p", v0="bob", v1="/item", v2="GET"))
+    s.add(CasbinRule(ptype="p", v0="data2_admin", v1="/item", v2="POST"))
+    s.add(CasbinRule(ptype="p", v0="data2_admin", v1="/item", v2="DELETE"))
+    s.add(CasbinRule(ptype="p", v0="data2_admin", v1="/item", v2="GET"))
+    s.add(CasbinRule(ptype="g", v0="alice", v1="data2_admin"))
+    s.add(CasbinRule(ptype="g", v0="users", v1="data2_admin"))
+    s.commit()
+    s.close()
+
+    return CasbinEnforcer(adapter=adapter)
+
+
+@pytest.fixture
+def enforcer(app_fixture):
+    e = enforcer_partial()
+    e.init_app(app_fixture)
+    yield e
+
+
+@pytest.fixture
+def watcher():
+    class SomeWatcher:
+        def should_reload(self):
+            return True
+
+        def update_callback(self):
+            pass
+
+    yield SomeWatcher
+
+
+@pytest.mark.parametrize(
+    "header, user, method, status, user_name",
+    [
+        ("X-User", "alice", "GET", 200, "X-User"),
+        ("X-USER", "alice", "GET", 200, "x-user"),
+        ("x-user", "alice", "GET", 200, "X-USER"),
+        ("X-User", "alice", "GET", 200, "X-USER"),
+        ("X-User", "alice", "GET", 200, "X-Not-A-Header"),
+        ("X-User", "alice", "POST", 201, None),
+        ("X-User", "alice", "DELETE", 202, None),
+        ("X-User", "bob", "GET", 200, None),
+        ("X-User", "bob", "POST", 401, None),
+        ("X-User", "bob", "DELETE", 401, None),
+        ("X-Idp-Groups", "admin", "GET", 401, "X-User"),
+        ("X-Idp-Groups", "users", "GET", 200, None),
+        ("X-Idp-Groups", "noexist,testnoexist,users", "GET", 200, None),
+        ("X-Idp-Groups", "noexist testnoexist users", "GET", 200, None),
+        ("X-Idp-Groups", "noexist, testnoexist, users", "GET", 200, None),
+        ("Authorization", "Basic Ym9iOnBhc3N3b3Jk", "GET", 200, "Authorization"),
+        ("Authorization", "Unsupported Ym9iOnBhc3N3b3Jk", "GET", 401, None),
+    ],
+)
+def test_enforcer(app_fixture, enforcer, header, user, method, status, user_name):
+    # enable auditing with user name
+    if user_name:
+        enforcer.user_name_headers = {user_name}
+
+    @app_fixture.route("/")
+    @enforcer.enforcer
+    def index():
+        return jsonify({"message": "passed"}), 200
+
+    @app_fixture.route("/item", methods=["GET", "POST", "DELETE"])
+    @enforcer.enforcer
+    def item():
+        if request.method == "GET":
+            return jsonify({"message": "passed"}), 200
+        elif request.method == "POST":
+            return jsonify({"message": "passed"}), 201
+        elif request.method == "DELETE":
+            return jsonify({"message": "passed"}), 202
+
+    headers = {header: user}
+    c = app_fixture.test_client()
+    # c.post('/add', data=dict(title='2nd Item', text='The text'))
+    rv = c.get("/")
+    assert rv.status_code == 401
+    caller = getattr(c, method.lower())
+    rv = caller("/item", headers=headers)
+    assert rv.status_code == status
+
+
+@pytest.mark.parametrize(
+    "header, user, method, status",
+    [
+        ("X-User", "alice", "GET", 200),
+        ("X-User", "alice", "POST", 201),
+        ("X-User", "alice", "DELETE", 202),
+        ("X-User", "bob", "GET", 200),
+        ("X-User", "bob", "POST", 401),
+        ("X-User", "bob", "DELETE", 401),
+        ("X-Idp-Groups", "admin", "GET", 401),
+        ("X-Idp-Groups", "users", "GET", 200),
+        ("Authorization", "Basic Ym9iOnBhc3N3b3Jk", "GET", 200),
+        ("Authorization", "Unsupported Ym9iOnBhc3N3b3Jk", "GET", 401),
+    ],
+)
+def test_enforcer_with_watcher(
+    app_fixture, enforcer, header, user, method, status, watcher
+):
+    enforcer.set_watcher(watcher())
+
+    @app_fixture.route("/")
+    @enforcer.enforcer
+    def index():
+        return jsonify({"message": "passed"}), 200
+
+    @app_fixture.route("/item", methods=["GET", "POST", "DELETE"])
+    @enforcer.enforcer
+    def item():
+        if request.method == "GET":
+            return jsonify({"message": "passed"}), 200
+        elif request.method == "POST":
+            return jsonify({"message": "passed"}), 201
+        elif request.method == "DELETE":
+            return jsonify({"message": "passed"}), 202
+
+    headers = {header: user}
+    c = app_fixture.test_client()
+    # c.post('/add', data=dict(title='2nd Item', text='The text'))
+    rv = c.get("/")
+    assert rv.status_code == 401
+    caller = getattr(c, method.lower())
+    rv = caller("/item", headers=headers)
+    assert rv.status_code == status
+
+
+def test_manager(app_fixture, enforcer):
+    @app_fixture.route("/manager", methods=["POST"])
+    @enforcer.manager
+    def manager(manager):
+        assert isinstance(manager, Enforcer)
+        return jsonify({"message": "passed"}), 201
+
+    c = app_fixture.test_client()
+    c.post("/manager")
+
+
+def test_enforcer_set_watcher(enforcer, watcher):
+    assert enforcer.e.watcher is None
+    enforcer.set_watcher(watcher())
+    assert isinstance(enforcer.e.watcher, watcher)
+
+
+@pytest.mark.parametrize(
+    "owner, method, status",
+    [
+        (["alice"], "GET", 200),
+        (["alice"], "POST", 201),
+        (["alice"], "DELETE", 202),
+        (["bob"], "GET", 200),
+        (["bob"], "POST", 401),
+        (["bob"], "DELETE", 401),
+        (["admin"], "GET", 401),
+        (["users"], "GET", 200),
+        (["alice", "bob"], "POST", 201),
+        (["noexist", "testnoexist"], "POST", 401),
+    ],
+)
+def test_enforcer_with_owner_loader(app_fixture, enforcer, owner, method, status):
+    @app_fixture.route("/")
+    @enforcer.enforcer
+    def index():
+        return jsonify({"message": "passed"}), 200
+
+    @app_fixture.route("/item", methods=["GET", "POST", "DELETE"])
+    @enforcer.enforcer
+    def item():
+        if request.method == "GET":
+            return jsonify({"message": "passed"}), 200
+        elif request.method == "POST":
+            return jsonify({"message": "passed"}), 201
+        elif request.method == "DELETE":
+            return jsonify({"message": "passed"}), 202
+
+    @enforcer.owner_loader
+    def owner_loader():
+        return owner
+
+    c = app_fixture.test_client()
+    # c.post('/add', data=dict(title='2nd Item', text='The text'))
+    rv = c.get("/")
+    assert rv.status_code == 401
+    caller = getattr(c, method.lower())
+    rv = caller("/item")
+    assert rv.status_code == status