@Override
    public NamedBlobDb getNamedBlobDb() throws RestServiceException {
      if (namedBlobDb == null) {
        throw new RestServiceException("Named blob support not enabled", RestServiceErrorCode.BadRequest);
      }
      return namedBlobDb;
    }
If {@link RestUtils.InternalKeys#SIGNED_ID_METADATA_KEY} is set in the {@link RestRequest}, return a signed id.
Otherwise, return the provided blob ID.
@param restRequest the {@link RestRequest} that might contain the signed ID metadata.
@param blobId the blob ID to potentially sign.
@return the signed ID, if required. Otherwise, just the provided blob ID.
@throws RestServiceException if building the signed ID fails.
ambry-frontend/src/main/java/com/github/ambry/frontend/AmbryIdConverterFactory.java