Ally is a framework for building distributed services in a federated architecture. In a federation, nodes may occupy multiple, independent administrative domains, with complex trust relationships, connected by an asynchronous, wide-area network. We present a library that implements Byzantine fault-tolerant agreement, a critical building-block service in robust distributed systems, targeted at the federation model; threshold cryptography improves the basic agreement protocol with proactive, verifiable security and improved resilience to continuous attack.