From the homepage MyProxy is defined as
- MyProxy is open source software for managing X.509 Public Key Infrastructure (PKI) security credentials (certificates and private keys). MyProxy combines an online credential repository with an online certificate authority to allow users to securely obtain credentials when and where needed. Users run myproxy-logon to authenticate and obtain credentials, including trusted CA certificates and Certificate Revocation Lists (CRLs).
It is also used by other services such as PhedEX to perform proxy certificate renewal on behalf of users. An example of this process has been documented for the RAL MyProxy service but could easily be extended to other MyProxy servers.