Password-protected site's sign-in button does nothing

#What you are seeing

A visitor types the site password and selects Sign in, but nothing happens. The page stays on the sign-in screen.

Site sign in card with the site icon, the site name, a Password field and a Sign in button — Visitors see this screen before a password protected site loads anything else. Sign in is the button that seems to do nothing.

#Why it happens

Password sign-in runs in the visitor's browser, so it needs JavaScript and an up-to-date browser. With JavaScript turned off, the form cannot submit, and selecting Sign in has no effect.

#What to do

Ask the visitor to turn on JavaScript for the site, then sign in again.

If sign-in still fails, the page shows a general "Sign in failed. Please try again." alert. That is all it can tell the visitor, so it will not say why.

Everyone was signed out of my protected site at once

A platform update to the sign-in mechanism invalidates all existing sessions.

Saving Access settings fails with a generic error

There is a hidden cap of 12 access-configuration changes per hour per tenant, with no mess