How do I stop 'mdwrite wants to use the "metadata" keychain' prompts?

Suddenly I'm getting repeated (endless) prompts that

mdwrite wants to use the "metadata" keychain

and asking me to

please enter the keychain password.

but my password (I know the password for each of my keychains, my system, and their full history) is rejected.

How do I stop this (latest) irritation — without deleting my keychain data? Why won't my keychain(s) password(s) work?

macOS 10.13.2 (17C88)

I had the same problem. I opened my login keychain and searched for MetadataKeychain. I clicked show password and copied and pasted it into the dialog asking for the password.

It worked!