Allow password as a callable when using Postgres backend

databases/backends/postgres.py

@@ -44,7 +44,7 @@ def _get_dialect(self) -> Dialect:
     def _get_connection_kwargs(self) -> dict:
         url_options = self._database_url.options
 
-        kwargs = {}
+        kwargs = {}  # type: typing.Dict[str, typing.Any]
         min_size = url_options.get("min_size")
         max_size = url_options.get("max_size")
         ssl = url_options.get("ssl")
@@ -62,15 +62,15 @@ def _get_connection_kwargs(self) -> dict:
 
     async def connect(self) -> None:
         assert self._pool is None, "DatabaseBackend is already running"
-        kwargs = self._get_connection_kwargs()
-        self._pool = await asyncpg.create_pool(
+        kwargs = dict(
             host=self._database_url.hostname,
             port=self._database_url.port,
             user=self._database_url.username,
             password=self._database_url.password,
             database=self._database_url.database,
-            **kwargs,
         )
+        kwargs.update(self._get_connection_kwargs())
+        self._pool = await asyncpg.create_pool(**kwargs)
 
     async def disconnect(self) -> None:
         assert self._pool is not None, "DatabaseBackend is not running"

tests/test_connection_options.py

@@ -43,6 +43,24 @@ def test_postgres_explicit_ssl():
     assert kwargs == {"ssl": True}
 
 
+def test_postgres_no_extra_options():
+    backend = PostgresBackend("postgres://localhost/database")
+    kwargs = backend._get_connection_kwargs()
+    assert kwargs == {}
+
+
+def test_postgres_password_as_callable():
+    def gen_password():
+        return "Foo"
+
+    backend = PostgresBackend(
+        "postgres://:password@localhost/database", password=gen_password
+    )
+    kwargs = backend._get_connection_kwargs()
+    assert kwargs == {"password": gen_password}
+    assert kwargs["password"]() == "Foo"
+
+
 def test_mysql_pool_size():
     backend = MySQLBackend("mysql://localhost/database?min_size=1&max_size=20")
     kwargs = backend._get_connection_kwargs()