crypto: Add getters for the sender key in our sessions

matrix_sdk_crypto/src/olm/group_sessions/inbound.rs

@@ -188,6 +188,11 @@ impl InboundGroupSession {
             .expect("Can't export at the first known index")
     }
 
+    /// Get the sender key that this session was received from.
+    pub fn sender_key(&self) -> &str {
+        &self.sender_key
+    }
+
     /// Export this session at the given message index.
     pub async fn export_at_index(&self, message_index: u32) -> Option<ExportedRoomKey> {
         let session_key =

matrix_sdk_crypto/src/olm/session.rs

@@ -77,6 +77,11 @@ impl Session {
         Ok(plaintext)
     }
 
+    /// Get the sender key that was used to establish this Session.
+    pub fn sender_key(&self) -> &str {
+        &self.sender_key
+    }
+
     /// Encrypt the given plaintext as a OlmMessage.
     ///
     /// Returns the encrypted Olm message.