User context identifier (e.g., "standard_user", "admin")
Either the format ("json" | "form") or the data table
Optional data table if format is specified
When I k6 authenticate with the following url and request body as "standard_user":
| endpoint | username | password |
| /login | test_user | pass123 |
When I k6 authenticate with the following url and request body as "admin" with "form":
| endpoint | client_id | client_secret | grant_type |
| /token | my-app | secret123 | client_credentials |
Authenticates with the API using credentials from a data table. Supports both JSON (default) and form-urlencoded formats.