What is the right way to send a client certificate with every request made by the resttemplate in spring?

Here is example how to do this using RestTemplate and Apache HttpClient

You should define your own RestTemplate with configured SSL context:

@Bean
public RestTemplate restTemplate(RestTemplateBuilder builder) throws Exception {
    char[] password = "password".toCharArray();

    SSLContext sslContext = SSLContextBuilder.create()
            .loadKeyMaterial(keyStore("classpath:cert.jks", password), password)
            .loadTrustMaterial(null, new TrustSelfSignedStrategy()).build();

    HttpClient client = HttpClients.custom().setSSLContext(sslContext).build();
    return builder
            .requestFactory(new HttpComponentsClientHttpRequestFactory(client))
            .build();
}

 private KeyStore keyStore(String file, char[] password) throws Exception {
    KeyStore keyStore = KeyStore.getInstance("PKCS12");
    File key = ResourceUtils.getFile(file);
    try (InputStream in = new FileInputStream(key)) {
        keyStore.load(in, password);
    }
    return keyStore;
}

Now all remote calls performed by this template will be signed with cert.jks.
Note: You would need to put cert.jks into your classpath

@Autowired
private RestTemplate restTemplate;

public List<Info> getInfo() throws RestClientException, URISyntaxException {
    HttpEntity<?> httpEntity = new HttpEntity<>(null, new HttpHeaders());

    ResponseEntity<Info[]> resp = restTemplate.exchange(
            new URI(BASE_URL + "/Info"), HttpMethod.GET, 
            httpEntity, Info[].class);
    return Arrays.asList(resp.getBody());
}