diff --git a/moto/cognitoidp/models.py b/moto/cognitoidp/models.py
index 32d1afc6d..61af80169 100644
--- a/moto/cognitoidp/models.py
+++ b/moto/cognitoidp/models.py
@@ -1005,6 +1005,39 @@ class CognitoIdpBackend(BaseBackend):
                     "SECRET_BLOCK": session,
                 },
             }
+        elif auth_flow == "USER_PASSWORD_AUTH":
+            username = auth_parameters.get("USERNAME")
+            password = auth_parameters.get("PASSWORD")
+
+            user = user_pool.users.get(username)
+
+            if not user:
+                raise UserNotFoundError(username)
+
+            if user.password != password:
+                raise NotAuthorizedError("Incorrect username or password.")
+
+            if user.status == UserStatus["UNCONFIRMED"]:
+                raise UserNotConfirmedException("User is not confirmed.")
+
+            session = str(uuid.uuid4())
+            self.sessions[session] = user_pool
+
+            access_token, expires_in = user_pool.create_access_token(
+                client_id, username
+            )
+            id_token, _ = user_pool.create_id_token(client_id, username)
+            refresh_token = user_pool.create_refresh_token(client_id, username)
+
+            return {
+                "AuthenticationResult": {
+                    "IdToken": id_token,
+                    "AccessToken": access_token,
+                    "ExpiresIn": expires_in,
+                    "RefreshToken": refresh_token,
+                    "TokenType": "Bearer",
+                }
+            }
         elif auth_flow == "REFRESH_TOKEN":
             refresh_token = auth_parameters.get("REFRESH_TOKEN")
             if not refresh_token:
diff --git a/tests/test_cognitoidp/test_cognitoidp.py b/tests/test_cognitoidp/test_cognitoidp.py
index bcc34d3e0..18c9ac2d4 100644
--- a/tests/test_cognitoidp/test_cognitoidp.py
+++ b/tests/test_cognitoidp/test_cognitoidp.py
@@ -1923,6 +1923,73 @@ def test_initiate_auth_REFRESH_TOKEN():
     result["AuthenticationResult"]["AccessToken"].should_not.be.none
 
 
+@mock_cognitoidp
+def test_initiate_auth_USER_PASSWORD_AUTH():
+    conn = boto3.client("cognito-idp", "us-west-2")
+    result = user_authentication_flow(conn)
+    result = conn.initiate_auth(
+        ClientId=result["client_id"],
+        AuthFlow="USER_PASSWORD_AUTH",
+        AuthParameters={"USERNAME": result["username"], "PASSWORD": result["password"]},
+    )
+
+    result["AuthenticationResult"]["AccessToken"].should_not.be.none
+    result["AuthenticationResult"]["IdToken"].should_not.be.none
+    result["AuthenticationResult"]["RefreshToken"].should_not.be.none
+
+
+@mock_cognitoidp
+def test_initiate_auth_USER_PASSWORD_AUTH_user_not_found():
+    conn = boto3.client("cognito-idp", "us-west-2")
+    result = user_authentication_flow(conn)
+    with pytest.raises(ClientError) as ex:
+        conn.initiate_auth(
+            ClientId=result["client_id"],
+            AuthFlow="USER_PASSWORD_AUTH",
+            AuthParameters={"USERNAME": "INVALIDUSER", "PASSWORD": result["password"]},
+        )
+    err = ex.value.response["Error"]
+    err["Code"].should.equal("UserNotFoundException")
+
+
+@mock_cognitoidp
+def test_initiate_auth_USER_PASSWORD_AUTH_user_incorrect_password():
+    conn = boto3.client("cognito-idp", "us-west-2")
+    result = user_authentication_flow(conn)
+    with pytest.raises(ClientError) as ex:
+        conn.initiate_auth(
+            ClientId=result["client_id"],
+            AuthFlow="USER_PASSWORD_AUTH",
+            AuthParameters={
+                "USERNAME": result["username"],
+                "PASSWORD": "NotAuthorizedException",
+            },
+        )
+    err = ex.value.response["Error"]
+    err["Code"].should.equal("NotAuthorizedException")
+
+
+@mock_cognitoidp
+def test_initiate_auth_USER_PASSWORD_AUTH_unconfirmed_user():
+    conn = boto3.client("cognito-idp", "us-west-2")
+    username = str(uuid.uuid4())
+    password = str(uuid.uuid4())
+    user_pool_id = conn.create_user_pool(PoolName=str(uuid.uuid4()))["UserPool"]["Id"]
+    client_id = conn.create_user_pool_client(
+        UserPoolId=user_pool_id, ClientName=str(uuid.uuid4()), GenerateSecret=True,
+    )["UserPoolClient"]["ClientId"]
+    conn.sign_up(ClientId=client_id, Username=username, Password=password)
+
+    with pytest.raises(ClientError) as ex:
+        conn.initiate_auth(
+            ClientId=client_id,
+            AuthFlow="USER_PASSWORD_AUTH",
+            AuthParameters={"USERNAME": username, "PASSWORD": password},
+        )
+    err = ex.value.response["Error"]
+    err["Code"].should.equal("UserNotConfirmedException")
+
+
 @mock_cognitoidp
 def test_initiate_auth_for_unconfirmed_user():
     conn = boto3.client("cognito-idp", "us-west-2")