[FEATURE REQUEST] Add documentation for FTPeS (FTP with explicite SSL)

[markusd112]

If this is a new feature, describe what you would like.

Please add some informations about FTPS using explicite SSL in the AllSky documentation

e.g. in the troubleshooting section? https://htmlpreview.github.io/?https://raw.githubusercontent.com/AllskyTeam/allsky/master/html/documentation/troubleshooting/uploads.html

When setting PROTOCOL="ftps" the upload is done by lftp via FTP with implicite SSL (normally via tcp/990, tcp/989). FTP with implicite SSL is outdated, so you should use FTP with explicite SSL (FTPeS) instead. If you want to upload your data with FTP via explicite SSL you have to configure: PROTOCOL="ftp" LFTP_COMMANDS="set ftp:ssl-force yes"

FTPeS opens the initial session via FTP without encryption. After negotiation AUTH_TLS with the FTP-server a TLS session is initiated and your username and password are encrypted. The "ftp:ssl-force yes" option refuses to send password in clear when server does not support SSL.

To check the communication and the use of TLS you can enable debugging via: LFTP_COMMANDS="debug 999999;set ftp:ssl-force yes"