wso2 - How to Access the Client Header Request -

i getting data mobile client sending data in json sending values header wso2esb getting normal values using property

<property name="asset" expression="//asset/text()" scope="default"/> 

but how can header in esb using property not not working

<property name="username" expression="get-property('transport', 'accept')"/> 

how work revert me in advance

<property name="username" expression="get-property('transport', 'accept')"/> 

in configuration trying assign http header named 'accept' property named 'username'.

if 'username' want access http headers, should like:

<property name="some_name_here" expression="get-property('transport', 'username')"/>