Google Safe Browsing URL validation

[UTCGilligan]

Safe Browsing Lookup API checks all submitted URLs agains the Google list to prevent phishing and other unsafe links from being submitted.

• https://github.com/YOURLS/google-safe-browsing

[UTCGilligan]

After activation, the "Copy" overlay on the Sleeky frontend form did not appear. The API call seemed to work, but may interfere with the function of the Sleeky frontend.

• Test again with plain Vanilla YOURLS front page.
• If that works, see why (or why not, if it won't work with Sleeky)