authentication - How can I check if it is the same user in ASP.NET? -

this question not related asp.net specifically, more web applications in general.

i building web application wherein registering user. of taking in basic credentials first name, last name, etc of user. in website giving information free user has registered user finds website authentic , not fake website. after that, more information, user has pay.

the information site provides obsolete after sometime. so, when new user registers, he/she new information gets updated; old users have pay same new information.

my problem here once information gets obsolete same person can re-register different set of credentials , new information. want avoid happening.

so question here this: information should request user, or extract user, check same user not re-registering? or other way make possible.

i thinking of getting ip address of machine person registering , use check. user can use different machine re-register.

i lost here , not getting solution. checked on internet not find answer.

please let me know if need further information side.

you not find technical way prevent users registering multiple times. can use device, ip, email account , different credentials.

what can asking them send hard fake "offline" information, credit card number or photo of id. users may still able register multiple times way, not indefinitly. lose many possible clients way unwilling provide such information test account, not solution want.

my advice 1 of following two:

• limit information/service give out free users, if register again gain when pay.
• try bind them account in way lose if threw away. may example providing user rewards activity (real or virtual) or increasing experience based on history. take example: if registered again, lose reputation. users think twice if worth new content.