i need to have extra fields on the Requisition updated on Assignment DFF

Summary:i need to have extra fields on the Requisition updated on the offer as default value and updated assignment  DFF when candidate is moved to HR

Content (required):

i need to add one field "signing Authority" that will show on the requisition for the recruiter to fill while creating a position then it should show on the offer with the value enterd by the recruiter and it should be open for update. this value should be transferred to the assignment DFF Attribute which is created with the same name

so like i want custom value to flow from requisition to assignment