Add E-Signatures to Spring Boot

@RestController
public class ContractController {
    private final RestTemplate rest = new RestTemplate();

    @PostMapping("/send-contract")
    public ResponseEntity<String> send(@RequestBody Map<String, String> body) {
        HttpHeaders headers = new HttpHeaders();
        headers.set("Authorization", "Bearer " + System.getenv("SIGNBEE_API_KEY"));
        headers.setContentType(MediaType.APPLICATION_JSON);

        HttpEntity<Map<String, String>> entity = new HttpEntity<>(body, headers);
        ResponseEntity<String> response = rest.postForEntity(
            "https://signb.ee/api/send", entity, String.class);
        return response;
    }
}