devpi: Database contents leak

devpi is a Python package index staging server and packaging, testing, and release tool. Prior to 6.20.2 and 7.0.0b3, a server configured with the primary or deprecated master role allows an unauthenticated, modified GET request to the +changelog route because verify_primary does not reject a missing identity and therefore fails to require ReplicaIdentity. The response can disclose complete database content, including Argon2 password hashes and identifiers and salts for devpi-tokens; exposed hashes may be subject to dictionary attacks, and public tokens may assist attempts to derive the server secret. Large responses can also consume significant CPU, input/output capacity, and bandwidth. Servers using the standalone role are not exposed through replication, and an instance served exclusively through nginx with devpi-lockdown redirects the request to login with no known exploit. This issue is fixed in devpi-server versions 6.20.2 and 7.0.0b3.