When I try to join a wifi network, a popup appears on someone else’s phone asking them to share the password. How do I disable this feature?

It has nothing to do with Keychain either.

Turning it off will not affect the sharing since it comes from an unrelated iOS device. So turning keychain off does not affect the other device.

Best way to prevent it, is to keep the iOS devices away from each other or turn off bluetooth. Second, the device receiving the sharing request can simply ignore it and not share it. Eventually the prompt disappears from the screen.

Other than that, its very handy. When you with friends or relatives, you can easily connect to a Wifi network their devices have connected to previously without much fuss. Just bring the iOS devices near each other and presto, password shared.

No need to write it down, or spell it out or anything.

Unfortunately it does not seem like you can turn it off.

It appears to be an oversight on Apples part.

Send them some feedback:

https://www.apple.com/feedback/

You could try turning off Keychain on your phone.

1. Tap Settings > [your name] > iCloud. If you're using iOS 10.2 or earlier, tap Settings > iCloud.
2. Tap Keychain > Advanced.
3. Turn off Approve with Security Code.

No, it is a new feature that does not involve hotspots. If you come to my house and attempt to join my network my iPhone will alert me of this and I can grant you access to my network without actually giving you the password.

It sounds like you're trying to join someone else's iPhone Hotspot. Do you know the network you're trying to join? Is it public or does it have a lock next to it?

Thanks Phil