Nice layout, and I'm mostly ok with the API.

But! This is a big "but" for me, by the way. Stop storing the user/password in a cookie, and specially do not store anywhere in plain text (much more specially don't do that in the cookies!). I just did a SELECT * FROM moz_cookies WHERE baseDomain = 'coinroll.it'; on cookies.sqlite from Firefox and I see everything as clear as it can get.

My second issue is the limit of bets. Are you scared of someone suddenly getting lucky on < 1 and stealing all your pot ?

Nevertheless, congrats on making a decent API for it.