@spec auth_header(String.t()) :: String.t()

Returns the auth header value for the given token.

@spec configured?() :: boolean()

Checks if a valid auth token is configured.

@spec mask(String.t()) :: String.t()

Masks a token for safe display.

Shows only the first and last 4 characters.

@spec parse_npmrc(String.t()) :: String.t() | nil

Reads token from an .npmrc file content.

@spec read() :: String.t() | nil

Reads the auth token from environment or .npmrc.

@spec valid_format?(String.t()) :: boolean()

Validates token format.

npm tokens are typically UUIDs or base64-encoded strings.