code: public String getDefaultCredentials() throws IOException {
          String securityCredentialsList = readResource(SECURITY_CREDENTIALS_RESOURCE);
  
          securityCredentialsList = securityCredentialsList.trim();
          String[] securityCredentials = securityCredentialsList.split("\n");
          if (securityCredentials.length == 0) return null;
  
          String securityCredentialsName = securityCredentials[0];
  
          return readResource(SECURITY_CREDENTIALS_RESOURCE + securityCredentialsName);
      }
docs: Connects to the Amazon EC2 Instance Metadata Service to retrieve the
  default credential information (if any).
  
  @return The response from the Amazon EC2 Instance Metadata Service, or
  null if no credential information was available.
  
  @throws IOException
  If any problems are encountered while connecting to the
  Amazon EC2 Instance Metadata Service.