security: Allow KeyChain to sign interest using SHA256 digest

Change-Id: I729c5e32aeb1b9e78582becec1bc183aada6ee95
Refs: #2218
diff --git a/src/security/key-chain.hpp b/src/security/key-chain.hpp
index 0cc3cb3..5d348c4 100644
--- a/src/security/key-chain.hpp
+++ b/src/security/key-chain.hpp
@@ -226,12 +226,18 @@
   signByIdentity(const uint8_t* buffer, size_t bufferLength, const Name& identityName);
 
   /**
-   * @brief Set Sha256 weak signature for @param data
+   * @brief Set Sha256 weak signature for @p data
    */
   void
   signWithSha256(Data& data);
 
   /**
+   * @brief Set Sha256 weak signature for @p interest
+   */
+  void
+  signWithSha256(Interest& interest);
+
+  /**
    * @brief Generate a self-signed certificate for a public key.
    *
    * @param keyName The name of the public key
@@ -789,6 +795,6 @@
   return;
 }
 
-}
+} // namespace ndn
 
 #endif // NDN_SECURITY_KEY_CHAIN_HPP