code: private void setProxyCredentials(Run<?, ?> run) {
      	if (proxySettings != null && proxySettings.getFsProxyCredentialsId() != null) {
      		UsernamePasswordCredentials up = CredentialsProvider.findCredentialById(
      				proxySettings.getFsProxyCredentialsId(),
              		StandardUsernamePasswordCredentials.class,
              		run,
          			URIRequirementBuilder.create().build());
  			
      		if (up != null) {
      			proxySettings.setFsProxyUserName(up.getUsername());
          		proxySettings.setFsProxyPassword(up.getPassword());
      		}
      	}
      }
docs: Get credentials by the credentials id. Then set the user name and password into the SsePoxySetting.