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c762425ea7
Analysis of customer stalls revealed that the function `detail::hash_with_salt` (invoked by `passwords::check`) often blocks the reactor. Internally, this function uses the external `crypt_r` function to compute password hashes, which is CPU-intensive. This PR addresses the issue in two ways: 1) `sha-512` is now the only password hashing scheme for new passwords (it was already the common-case). 2) `passwords::check` is moved to a dedicated alien thread. Regarding point 1: before this change, the following hashing schemes were supported by `identify_best_supported_scheme()`: bcrypt_y, bcrypt_a, SHA-512, SHA-256, and MD5. The reason for this was that the `crypt_r` function used for password hashing comes from an external library (currently `libxcrypt`), and the supported hashing algorithms vary depending on the library in use. However: - The bcrypt schemes never worked properly because their prefixes lack the required round count (e.g. `$2y$` instead of `$2y$05$`). Moreover, bcrypt is slower than SHA-512, so it not good idea to fix or use it. - SHA-256 and SHA-512 both belong to the SHA-2 family. Libraries that support one almost always support the other, so it’s very unlikely to find SHA-256 without SHA-512. - MD5 is no longer considered secure for password hashing. Regarding point 2: the `passwords::check` call now runs on a shared alien thread created at database startup. An `std::mutex` synchronizes that thread with the shards. In theory this could introduce a frequent lock contention, but in practice each shard handles only a few hundred new connections per second—even during storms. There is already `_conns_cpu_concurrency_semaphore` in `generic_server` limits the number of concurrent connection handlers. Fixes https://github.com/scylladb/scylladb/issues/24524 Backport not needed, as it is a new feature. Closes scylladb/scylladb#24924 * github.com:scylladb/scylladb: main: utils: add thread names to alien workers auth: move passwords::check call to alien thread test: wait for 3 clients with given username in test_service_level_api auth: refactor password checking in password_authenticator auth: make SHA-512 the only password hashing scheme for new passwords auth: whitespace change in identify_best_supported_scheme() auth: require scheme as parameter for `generate_salt` auth: check password hashing scheme support on authenticator start