package com.github.davidmoten.aws.lw.client;
   
   import java.util.Optional;
   
   import com.github.davidmoten.aws.lw.client.internal.CredentialsImpl;
   import com.github.davidmoten.aws.lw.client.internal.Environment;
   
   public interface Credentials {
       
      String accessKey();
  
      String secretKey();
  
      Optional<String> sessionToken();
  
      static Credentials of(String accessKey, String secretKey) {
          return new CredentialsImpl(accessKey, secretKey, Optional.empty());
      }
      
      static Credentials of(String accessKey, String secretKey, String sessionToken) {
          return new CredentialsImpl(accessKey, secretKey, Optional.of(sessionToken));
      }
  
      static Credentials fromEnvironment() {
          return Environment.instance().credentials();
      }
      
      static Credentials fromSystemProperties() {
          return new CredentialsImpl(System.getProperty("aws.accessKeyId"),
                  System.getProperty("aws.secretKey"),
                  Optional.empty());
      }
  
  }