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

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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());
}

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