This page serves to document the various access mechanisms availible to the Minecraft web services.
Used to check if an account is premium or not. Returns true if the username is a premium Minecraft account, returns false otherwise. This should be used with caution as it has been slated for removal by Mojang.
http://session.minecraft.net/game/getversion.jsp?user=<USERNAME>&password=<PASSWORD>&version=12 OR http://login.minecraft.net/?user=<USERNAME>&password=<PASSWORD>&version=12 OR https://login.minecraft.net/?user=<USERNAME>&password=<PASSWORD>&version=12
The Minecraft launcher uses this to authenticate logins. If the username and password are valid for a premium account, returns "<POSIX time>:<hash of password???>:<username with correct capitalization>:<freshly generated session id>:<UID (Presently unused)>". If username and password are invalid, returns "Bad login". If the username and password are correct, but the account isn't premium, returns "User not premium". If the given version number is less than 12, returns "Old version". The username is not case-sensitive, but naturally, the password is. Both GET and POST methods are supported.
This link seems to be called when a server with online-mode=true checks if it should allow a player to join the game. The session ID is generated by the launcher when you log in (you can also generate them with the "getversion.jsp" link above). This URL will return "OK" if the given session ID is the last one to have been generated for that username; otherwise it will return "Bad login".
Returns the skin for a given username. Case-sensitive, returns an HTTP 404 error if the skin doesn't exist.
Returns the skin for a given username. Case-sensitive, returns an HTTP 404 error if the user does not have a cape.
This is used to create the classic server list. It is documented properly on Classid Protocol
A test page that Mojang asked people to use as they worked on a new launcher for Minecraft. Runs a few processes in the browser, then starts a new version of the launcher, which will be downloaded to /.minecraft/launcher as launcher.jar (only known difference between this launcher and the normal one - this launcher has the new logo)
This link gives a glimpse at a future feature to Minecraft. This page says that, in the future, it will be possible to have Minecraft open and connect to the server IP specified in the URL when you access this link. See it for yourself!
Apparently some sort of joke page. It says it is triangulating a satellite and sending benchmark data back to Mojang or whatever, but a look at the source shows it is just an animation. This page no longer functions.