content: package com.alibaba.sdk.android.oss.common.auth;
  
  /**
   * Created by zhouzhuo on 11/4/15.
   */
  public abstract class OSSCustomSignerCredentialProvider implements OSSCredentialProvider {
      /**
       * Custom content sign method. Considering the AccessKeyId/AccessKeySecret is not likely be stored in mobile device,
       * this method is supposed to talk to customer's app servers and get the signature of the content.
       * The typical implementation could be that it posts the content to an app servers and the server has the AK information
       * and sign the content then return the signature.
       * <p>
       * The sign algorithm：http://help.aliyun.com/document_detail/oss/api-reference/access-control/signature-header.html
       * signature = "OSS " + AccessKeyId + ":" + base64(hmac-sha1(AccessKeySecret, content))
       * <p>
       * <p>
       * content is the final text to sign which comes from the URL parameters, headers and the actual content payload.
       *
       * @param content The final text to sign, which is concated from url parameters, url headers and body.
       * @return "OSS " + AccessKeyId + ":" + base64(hmac-sha1(AccessKeySecret, content))
       */
      public abstract String signContent(String content);
  
      @Override
      public OSSFederationToken getFederationToken() {
          return null;
      }
  }
  