add use_ssl doc (#349)

Author: baermat

src/content/docs/aws/services/cognito-idp.mdx

@@ -347,6 +347,8 @@ curl \
 {"access_token": "eyJ0eXAi…lKaHx44Q", "expires_in": 86400, "token_type": "Bearer", "refresh_token": "e3f08304", "id_token": "eyJ0eXAi…ADTXv5mA"}
 ```
 
+If your use case requires it, you can enforce https in URLs used by the auth flow by setting the environment variable `USE_SSL=1` 
+
 ### Client credentials grant
 
 The client credentials grant is designed for machine-to-machine (M2M) communication.