Non-secret description of a stored credential. list-secrets returns
these; the material is never included, so enumerating what exists
leaks nothing that could be used to authenticate.
Shape of a secret, as a namespaced string. Well-known kinds carry the
std: prefix and are registered in ACT-CONSTANTS: “std:opaque” (one
value), “std:basic” (username and password), “std:oauth2” (an access
token, with expiry and scopes alongside it); third-party kinds use
their own namespace. The kind determines which keys appear in
secret.fields.