* obtaining a token and logging in using the provided credentials.
 *
 * <p>This class supports both GET and POST methods for token and login
 * requests. It also allows for the replacement of placeholders in URLs and
 * parameters with actual credentials.
 *
 * <p>Usage example:
 * <pre>
 * {@code
 * Map<String, String> params = new HashMap<>();
 * params.put("token_url", "http://example.com/token");