A provider network implements a proxy to control access to web-based resources of a provider network. The proxy receives requests to access web-based services. The proxy allows access to a web-based service only if user-configured access control rules are satisfied and credentials associated with the web-based service are authenticated. The proxy prevents access to a web-based service if user-configured access control rules are not satisfied or credentials associated with the web-based service are not authenticated. The provider network may also implement a proxy configuration service to set up and launch the proxy. The proxy configuration service receives from the client a specification of the access control rules, configures the proxy based on the access control rules, and launches the proxy.