The embodiments described herein generally relate to methods and systems for tunneling arbitrary binary data between an HTTP endpoint and an arbitrary destination. Such tunneling of data is valuable in an environment, for example, in which a browser-based client communicates in the HTTP protocol and desires to exchange data with a remote endpoint understanding non-HTTP communications. A relay server is used as a “middle man” to connect the client to the destination, and components supporting the necessary protocols for data exchange are plugged into the relay server. To achieve reliable and ordered transmission of data, the relay server groups sessions through the assignment of session identifiers and tracks the exchange of messages through the assignment of sequence and acknowledgment numbers. Further, the relay server provides for authenticating the HTTP endpoint with the destination and for handling other operations not available in the constrained environment of the Web-based client.