\documentclass{article}
\usepackage{glossaries}
\newacronym{fs}{FS}{forward secrecy}
\newacronym{pfs}{PFS}{perfect \gls{fs}}
\newacronym{http}{HTTP}{Hypertext Transfer Protocol}
\newacronym{https}{HTTPS}{\gls{http} Secure}
\begin{document}
\Gls{pfs}
\Gls{https}
\end{document}
