Secrets Via Environment

Pass credentials through the environment so they never appear in process arguments or config files

Use when: a tool server needs a token to call an external service on the agent's behalf

Avoid when: the server needs no credential and reads only local files

Procedure

1. Identify every credential the server needs at runtime
2. Read each one from the environment inside the server, failing clearly when absent
3. Keep the value out of argv, config files and log lines
4. Ensure error messages never echo the value back
5. Set the variables in the launching environment, not in a committed file
6. Verify the server refuses to start when a required variable is missing

Signals

• the server fails fast with a message naming the missing variable, not its value
• process listings show no credential
• logs contain no token material after a failure
• the config file holds a reference, never the secret

Patterns

1. Read at startup

token = os.environ["HUNT_TOKEN"]

2. Clear failure

missing HUNT_TOKEN in environment; refusing to start

3. Redacted log

token: [set] or [unset]

Pitfalls

• Passing a token as a command line argument where every process can read it
• Logging the full request headers when an error occurs
• Using a default placeholder secret that silently works in production

Done when

• no credential appears in argv, config or logs
• a missing variable produces a clear startup failure

References

• OWASP - secrets management
• MCP - security best practices