Authentication material is any information a system uses to prove identity or authorize access. Common examples include passwords, API keys, session tokens, certificates, and one-time codes. In practice, the system treats this material as evidence that the caller is allowed to act as a specific user, service, or device.
It matters because exposed authentication material can turn into immediate abuse. If an API key or token is stolen, copied, or reused, an attacker may be able to make valid requests, read data, or change settings without triggering obvious login failures. Defenders reduce this risk by rotating secrets, revoking compromised credentials, limiting privileges, and monitoring for unusual use. In incidents involving leaked payment or cloud credentials, the key issue is often not the file itself but the authentication material inside it.