Merge #3274

3274: Reject master keys that are less than 16 bytes and add `--generate-master-key` CLI option r=irevoire a=dureuill

# Pull Request

## Related issue
Fix #3272 
Fix #3287

## What does this PR do?

### User standpoint

---

- Adds a `--generate-master-key` CLI flag to generate a fresh Master Key and exit.

<img width="1351" alt="Capture d’écran 2022-12-22 à 14 18 58" src="https://user-images.githubusercontent.com/41078892/209142778-eab52eeb-eaa8-409b-897a-c0d5728c8aaa.png">

---

(relevant fragment of the `--help` message)

<img width="1351" alt="Capture d’écran 2022-12-22 à 14 19 40" src="https://user-images.githubusercontent.com/41078892/209142891-ebfa2ed6-f231-4f76-a3ae-b7542c7aef04.png">

---

- When `meilisearch` is started in the `development` environment and no Master Key has been provided, then the binary prints a warning before starting.

<img width="1351" alt="Capture d’écran 2022-12-22 à 14 14 49" src="https://user-images.githubusercontent.com/41078892/209142158-54eba3b7-bf71-4f3f-8840-0600b13a1a9f.png">

---

- When `meilisearch` is started in the `development` environment and the provided Master Key is shorter than 16 bytes, then the binary prints a warning before starting.

<img width="1351" alt="Capture d’écran 2022-12-22 à 14 15 58" src="https://user-images.githubusercontent.com/41078892/209142295-0209fe47-c03b-424f-a73f-cee9b633137a.png">

---

- When `meilisearch` is started in the `production` environment, and no Master Key is provided, the error message is altered to generate a fresh Master Key.

<img width="1351" alt="Capture d’écran 2022-12-22 à 17 29 02" src="https://user-images.githubusercontent.com/41078892/209180540-0def5798-15db-47f0-a6ec-8cfa081dea77.png">


---

- When `meilisearch` is started in the `production` environment, and the provided Master Key is shorter than 16 bytes, then the binary exits with an error.

<img width="1351" alt="Capture d’écran 2022-12-22 à 17 28 47" src="https://user-images.githubusercontent.com/41078892/209180567-fa54fe33-fbc4-4b9f-b281-7dfb7b33af85.png">


---

This implements the solution B described here: https://github.com/meilisearch/product/discussions/538#discussioncomment-4391346 

### Implementation standpoint

- Add a new `meilisearch-auth::generate_master_key` function that uses a Cryptographic Random Number Generator (CRNG) to fill a vector of 32 bytes before encoding these bytes as base64

## PR checklist
Please check if your PR fulfills the following requirements:
- [x] Does this PR fix an existing issue, or have you listed the changes applied in the PR description (and why they are needed)?
- [x] Have you read the contributing guidelines?
- [x] Have you made sure that the title is accurate and descriptive of the changes?

Thank you so much for contributing to Meilisearch!


Co-authored-by: Louis Dureuil <louis@meilisearch.com>
Co-authored-by: Tamo <tamo@meilisearch.com>

Cargo.lock

@@ -2352,6 +2352,7 @@ dependencies = [
 name = "meilisearch-auth"
 version = "1.0.0"
 dependencies = [
+ "base64",
  "enum-iterator",
  "hmac",
  "meilisearch-types",

meilisearch-auth/Cargo.toml

@@ -4,6 +4,7 @@ version = "1.0.0"
 edition = "2021"
 
 [dependencies]
+base64 = "0.13.1"
 enum-iterator = "1.1.3"
 hmac = "0.12.1"
 meilisearch-types = { path = "../meilisearch-types" }

meilisearch-auth/src/lib.rs

@@ -268,3 +268,20 @@ fn generate_default_keys(store: &HeedAuthStore) -> Result<()> {
 
     Ok(())
 }
+
+pub const MASTER_KEY_MIN_SIZE: usize = 16;
+const MASTER_KEY_GEN_SIZE: usize = 32;
+
+pub fn generate_master_key() -> String {
+    use rand::rngs::OsRng;
+    use rand::RngCore;
+
+    // We need to use a cryptographically-secure source of randomness. That's why we're using the OsRng; https://crates.io/crates/getrandom
+    let mut csprng = OsRng;
+    let mut buf = vec![0; MASTER_KEY_GEN_SIZE];
+    csprng.fill_bytes(&mut buf);
+
+    // let's encode the random bytes to base64 to make them human-readable and not too long.
+    // We're using the URL_SAFE alphabet that will produce keys without =, / or other unusual characters.
+    base64::encode_config(buf, base64::URL_SAFE_NO_PAD)
+}

meilisearch/src/analytics/segment_analytics.rs

@@ -277,6 +277,7 @@ impl From<Opt> for Infos {
             indexer_options,
             scheduler_options,
             config_file_path,
+            generate_master_key: _,
             #[cfg(all(not(debug_assertions), feature = "analytics"))]
                 no_analytics: _,
         } = options;

meilisearch/src/main.rs

@@ -8,7 +8,7 @@ use actix_web::HttpServer;
 use index_scheduler::IndexScheduler;
 use meilisearch::analytics::Analytics;
 use meilisearch::{analytics, create_app, setup_meilisearch, Opt};
-use meilisearch_auth::AuthController;
+use meilisearch_auth::{generate_master_key, AuthController, MASTER_KEY_MIN_SIZE};
 
 #[global_allocator]
 static ALLOC: mimalloc::MiMalloc = mimalloc::MiMalloc;
@@ -33,16 +33,36 @@ async fn main() -> anyhow::Result<()> {
 
     setup(&opt)?;
 
-    match opt.env.as_ref() {
-        "production" => {
-            if opt.master_key.is_none() {
+    if opt.generate_master_key {
+        println!("{}", generate_master_key());
+        return Ok(());
+    }
+
+    match (opt.env.as_ref(), &opt.master_key) {
+        ("production", Some(master_key)) if master_key.len() < MASTER_KEY_MIN_SIZE => {
             anyhow::bail!(
-                    "In production mode, the environment variable MEILI_MASTER_KEY is mandatory"
+                "In production mode, the master key must be of at least {MASTER_KEY_MIN_SIZE} characters, but the provided key is only {} characters long
+
+We generated a secure Master Key for you (you can safely copy this token):
+
+>> export MEILI_MASTER_KEY={} <<",
+                master_key.len(),
+                generate_master_key(),
             )
         }
+        ("production", None) => {
+            anyhow::bail!(
+                "In production mode, you must provide a master key to secure your instance. It can be specified via the MEILI_MASTER_KEY environment variable or the --master-key launch option.
+
+We generated a secure Master Key for you (you can safely copy this token):
+
+>> export MEILI_MASTER_KEY={} <<
+",
+                generate_master_key()
+            )
         }
-        "development" => (),
-        _ => unreachable!(),
+        // No error; continue
+        _ => (),
     }
 
     let (index_scheduler, auth_controller) = setup_meilisearch(&opt)?;
@@ -151,11 +171,29 @@ Anonymous telemetry:\t\"Enabled\""
 
     eprintln!();
 
-    if opt.master_key.is_some() {
+    match (opt.env.as_ref(), &opt.master_key) {
+        ("production", Some(_)) => {
             eprintln!("A Master Key has been set. Requests to Meilisearch won't be authorized unless you provide an authentication key.");
-    } else {
-        eprintln!("No master key found; The server will accept unidentified requests. \
-            If you need some protection in development mode, please export a key: export MEILI_MASTER_KEY=xxx");
+        }
+        ("development", Some(master_key)) => {
+            eprintln!("A Master Key has been set. Requests to Meilisearch won't be authorized unless you provide an authentication key.");
+
+            if master_key.len() < MASTER_KEY_MIN_SIZE {
+                eprintln!();
+                log::warn!(
+                    "The provided Master Key is too short (< {MASTER_KEY_MIN_SIZE} characters)"
+                );
+                eprintln!("A Master Key of at least {MASTER_KEY_MIN_SIZE} characters will be required when switching to the production environment.");
+                eprintln!("Restart Meilisearch with the `--generate-master-key` flag to generate a secure Master Key you can use");
+            }
+        }
+        ("development", None) => {
+            log::warn!("No master key found; The server will accept unidentified requests");
+            eprintln!("If you need some protection in development mode, please export a key:\n\nexport MEILI_MASTER_KEY={}", generate_master_key());
+            eprintln!("\nA Master Key of at least {MASTER_KEY_MIN_SIZE} characters will be required when switching to the production environment.");
+        }
+        // unreachable because Opt::try_build above would have failed already if any other value had been produced
+        _ => unreachable!(),
     }
 
     eprintln!();

meilisearch/src/option.rs

@@ -49,6 +49,7 @@ const MEILI_IGNORE_MISSING_DUMP: &str = "MEILI_IGNORE_MISSING_DUMP";
 const MEILI_IGNORE_DUMP_IF_DB_EXISTS: &str = "MEILI_IGNORE_DUMP_IF_DB_EXISTS";
 const MEILI_DUMP_DIR: &str = "MEILI_DUMP_DIR";
 const MEILI_LOG_LEVEL: &str = "MEILI_LOG_LEVEL";
+const MEILI_GENERATE_MASTER_KEY: &str = "MEILI_GENERATE_MASTER_KEY";
 #[cfg(feature = "metrics")]
 const MEILI_ENABLE_METRICS_ROUTE: &str = "MEILI_ENABLE_METRICS_ROUTE";
 
@@ -230,6 +231,13 @@ pub struct Opt {
     #[serde(default = "default_log_level")]
     pub log_level: String,
 
+    /// Generates a string of characters that can be used as a master key and exits.
+    ///
+    /// Pass the generated master key using the `--master-key` argument or the `MEILI_MASTER_KEY` environment variable in a subsequent Meilisearch invocation.
+    #[clap(long, env = MEILI_GENERATE_MASTER_KEY)]
+    #[serde(default)]
+    pub generate_master_key: bool,
+
     /// Enables Prometheus metrics and /metrics route.
     #[cfg(feature = "metrics")]
     #[clap(long, env = MEILI_ENABLE_METRICS_ROUTE)]
@@ -328,6 +336,7 @@ impl Opt {
             ignore_missing_snapshot: _,
             ignore_snapshot_if_db_exists: _,
             import_dump: _,
+            generate_master_key: _,
             ignore_missing_dump: _,
             ignore_dump_if_db_exists: _,
             config_file_path: _,