Although I have not implemented captcha in any login form, but , i do have some fair idea of it. So i am sharing my thoughts on it
a. captcha is any randon alphanumeric string used for authentication in login form. We can write a simple java class to generate random
aplhanumeric strings which can be shown on jsp page. I assume you know how to display a captcha string on jsp page and use it in validation in furthur processing after form submission.
Below mentioned is the link of a pdf from "Spring in Practice" book by Manning publication.
Refer to section 4.4 Use CAPTCHAs to prevent automated user account creation where it is mentioned how to use captcha in spring login form.
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posted 8 years ago
I have already done it.
I have used reCaptcha, no problems here. Main problem was to intercept authentication process to check captcha and reject authentication whenever that is necessary. I don't know if my way is the best one, so if there is better solution I would like to hear it . I had to declare my own authentication provider sublassed from DaoAuthenticationProvider and there I overrode additionalAuthenticationChecks, that is a place where I verify captcha. Moreover I subclassed WebAuthenticationDetails to save captcha from request for subsequent verification. That was a bit difficult to tie together, as I am new to spring and had to search internet for lots of things.
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