Update IETF-RFC.md

Co-authored-by: Giuseppe Lo Presti <giuseppe.lopresti@cern.ch>

Author: mickenordin

IETF-RFC.md

@@ -464,7 +464,8 @@ If the Recieving Party knows of a resource that has not yet been shared, the Rec
 * using [httpsig](https://datatracker.ietf.org/doc/html/draft-cavage-http-signatures-12)
 
 ## Fields
-
+* REQUIRED sender (string)
+          OCM Address of the user who will be requested to share the resource.
 * REQUIRED shareWith (string) 
           OCM Address of the user, group or federation that
           wants to receive a share of the resource.