The <input type="hidden" name="__VIEWSTATE" id="__VIEWSTATE" of the page contains text, ordering the letter by their frequency we obtain the reverse of the lexicographic order, so there is some pattern there.
Ordering by frequencies, j code where u is the hidden text (~. u) /: +/"1 (~. u) I."(0 1) u
zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA=9876543210/+
The text asfasfasdfasfdasdfasfasfasfsadffffffffffffffffffffasdfsfsafsfdwfgasdgbdfbgdsgasdgdsbdb
could be a base seven number (and seven letters) that could be used to generate some permutation or pattern to reveal the hidden message. Trying the permutations with A. in J don't give good results so the seven letters could mean some kind of cut to the text to determine fragments. Just some ideas.
I don't like being downvoted so this user will be removed (by changing the password to be a random password)