Add support for ALTCHA

[mfelczak]

ALTCHA is a free, open source, and self-hosted alternative to reCaptcha. It's also more accessible since it doesn't require any user interaction. Github repo: https://github.com/altcha-org/altcha

[mfelczak]

Hello @asmecher, before we start implementation I wanted to confirm recommended approach with you: should this be modelled on the existing reCaptcha implementation with install-wide settings in config.inc.php and a corresponding FormValidator subclass?

[asmecher]

Hi Michael -- Yes, on balance I think that's best. If we are going to have several options then in my wildest dreams we'd have an interface that all options could meet, but if it's just two options (ALTCHA and ReCAPTCHA) then there's not enough benefit to justify the overhead in coding.

[Godoy0722]

I just implemented ALTCHA integration for login, register and reset password pages. You can see it on #10456.

For this support to work, the config.inc.php must be updated with the new variables as I also created PRs as follows:

• OPS/775
• OJS/4446
• OMP/1703

To Reproduce
Steps to reproduce the behavior:

1. Starting on the root directory of any system, Run composer --working-dir=lib/pkp install
2. Update the config.inc.php file with the new variables as shown on the other PRs, and set altcha and altcha_on_login as on
3. Enter on login page and click on submit button

[Godoy0722]

@asmecher just a heads-up that the PRs are ready to be reviewed!