oauth2-proxy base64-decodes cookie_secret and requires it to decode to 16/24/32
bytes. Plain 'openssl rand -base64 32' yields 44 chars of standard base64
(padding + possibly '+/'), which it cannot decode and treats as 44 raw bytes,
failing with 'cookie_secret must be 16, 24, or 32 bytes ... but is 44 bytes'.
Use URL-safe, unpadded base64 instead (secrets.token_urlsafe(32) or the
openssl|tr variant).
Co-authored-by: SREDevOpsAgents <agents@sredevops.org>