code: public ClientBuilder iamApiKey(String iamApiKey, String iamServerClientId,
                                     String iamServerClientSecret) {
          this.iamApiKey = iamApiKey;
          this.iamServerClientId = iamServerClientId;
          this.iamServerClientSecret = iamServerClientSecret;
          return this;
      }
docs: Sets the
  <a href="https://console.bluemix.net/docs/services/Cloudant/guides/iam.html#ibm-cloud-identity-and-access-management"
  target="_blank">IAM</a> API key for the client connection. Also allows a client ID and secret
  to be specified for use when authenticating with the IAM token server.
  <P>
  Example creating a {@link CloudantClient} using IAM authentication:
  </P>
  <pre>
  {@code
  CloudantClient client = ClientBuilder.account("yourCloudantAccount")
  .iamApiKey("yourIamApiKey", "yourClientId", "yourClientSecret")
  .build();
  }
  </pre>
  
  @param iamApiKey the IAM API key for the session
  @param iamServerClientId Client ID used to authenticate with IAM token server
  @param iamServerClientSecret Client secret used to authenticate with IAM token server
  @return this ClientBuilder object for setting additional options