I have found a lot of posts about this, but cannot find the one that points me on the right direction. What I really need, further than connecting a file manager to ISPConfig, is a method for uploading a single compressed file and then uncompressing it, in a way that is enough intuitive to offer to my clients (people that can handle a filezilla-like program but that are not able to connect via SSH and execute several commands). The goal is to upload a file and to uncompress it in the server, and the uncompression has to occur directly on the server (otherwise a file-by-file upload will still ocurring, which is the thing to avoid to save time and errors uploading files). I know there is a lot of post dealing with this, but I could not find a final solution for this. I would be please I you can point me in the right direction, or share some links I have missed. Thanks a lot.
You can do this with most web FTP clients, e.g., with net2ftp. Install a web FTP client on your server, then login to ISPConfig and set the URL to the webftp client you installed under system > interface > main config > Sites > WebFTP URL
Passwords are securely encrypted with one-way hashes, so ISPConfig does not know the cleartext password or can retrieve it to pass it to the FTP client.