Stop storing API keys in plaintext

[fblundun]

In case an unauthorized person gets access to a backup of the database or discovers a SQL injection vulnerability, the keys should be hashed. We could investigate using bcrypt.

A lot of security measures (e.g. salt and pepper) seem to exist to protect users who have low-entropy passwords. Since the API keys are already 128-bit UUIDs I don't know whether these measures are necessary. But maybe somebody who knows more about cryptography will put me right.

[alexanderdean]

For reference matomo-org/matomo#5728

[fblundun]

This answer supports my claim above that protection for our API keys doesn't need to be as sophisticated as protection for a human-generated password.

[alexanderdean]

What a great answer!