Introduce the --generate-master-key cli-flag

[irevoire]

Associated issue; meilisearch/meilisearch#3287
Associated PR; #209

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Summary

Introduce the --generate-master-key cli-flag.
It generates a cryptographically safe to use master-key.

Changes

Introduce the --generate-master-key cli-flag

Attention To Reviewers

Should we really introduce an env-var + allow this parameter to be specified with the config file?

[gmourier]

LGTM! Thank you @irevoire.

Edit: I approved to fast 😇

[gmourier]

Could we indicate the message being shown when generate-master-key is used?

About the Attention To Reviewers questions, it doesn't shock me to keep something consistent (i.e. it can be used as env var but also in the configuration file).

The only concern I have is that a user may be stuck without knowing how to disable the generation of a master key. One idea could be to indicate in the message that the master-key is given without launching the instance because generate-master-key is used. WDYT?

[irevoire]

Currently, only the master-key is outputted with no text at all. This allows you to run something like meilisearch --generate-master-key | xargs meilisearch --db-path truc --master-key.
Or more generally, export MEILI_MASTER_KEY=$(meilisearch --generate-master-key).
I don't know if it's really important.

One idea could be to indicate in the message that the master-key is given without launching the instance because generate-master-key is used.

It's ok-ish to me.

Another idea could be to make the --generate-master-key incompatible with settings your master-key so people would get a better error message once they start to run their meilisearch 🤔

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The last solution I can think of is to output the master-key in the logs and thus when you use the --generate-master-key it starts meilisearch.
But I think there is a security concern with this one, people would not be able to share their logs anymore and even storing them would get complicated 😩

[gmourier]

But I think there is a security concern with this one, people would not be able to share their logs anymore and even storing them would get complicated 😩

💯

I've been thinking about it again, and IMO it's perfectly ok to go as that for v1.0

1. This flag is a bonus. The user flow already indicates pre-generated master keys when possible. See the different screenshots (Regarding that we could always output a generated master key plus give the helper to generate another one by hand to be more consistent)
2. We'll see if keeping it as such (just outputting a master key) is a problem depending on user feedback we may collect.

[dureuill]

I'd like to call your attention on the fact that there are currently discussions (internal link) about removing this flag.

[gmourier]

Closing following meilisearch/meilisearch#3308

Removal of this option proceeds of the following reasoning:

1. It is the only option that starts meilisearch and then immediately exits
2. We are unsure if we want to keep it under this form in the future or switch to a subcommand.
3. Releasing this option in v1 would make it insta-stable.
4. The option is only marginally useful, as users will be presented with freshly generated key directly in the error messages if their master key is absent/too short.
5. If we remove this option now, we can still add it back in a future v1 release. If we add it now, we won't be able to remove it in any future v1 version.