Centrifugo: SSRF via unverified JWT claims interpolated into dynamic JWKS endpoint URL

Centrifugo is an open-source scalable real-time messaging server. Prior to 6.7.0, Centrifugo is vulnerable to Server-Side Request Forgery (SSRF) when configured with a dynamic JWKS endpoint URL using template variables (e.g. {{tenant}}). An unauthenticated attacker can craft a JWT with a malicious iss or aud claim value that gets interpolated into the JWKS fetch URL before the token signature is verified, causing Centrifugo to make an outbound HTTP request to an attacker-controlled destination. This vulnerability is fixed in 6.7.0.