How should I exclude content?

[EcommerceSite]

I have category pages on an e-commerce site that are showing up as duplicate pages. On top of each page are register and login, and when selected they come up as category/login and category/register. I have 3 options to attempt to fix this and was wondering what you think is the best.

1. Use robots.txt to exclude. There are hundreds of categories so it could become large.

2. Use canonical tags.

3. Force Login and Register to go to their own page.

[SanketPatel]

Its not going to harm your website but if you really want fix it out then put "noindex" meta robot tag into those pages ( 4th option).