code: func (n *Network) PeerUserKey(p *Peer, user string) string {
  	org := n.Organization(p.Organization)
  	Expect(org).NotTo(BeNil())
  
  	keystore := filepath.Join(
  		n.PeerUserMSPDir(p, user),
  		"keystore",
  	)
  
  	// file names are the SKI and non-deterministic
  	keys, err := ioutil.ReadDir(keystore)
  	Expect(err).NotTo(HaveOccurred())
  	Expect(keys).To(HaveLen(1))
  
  	return filepath.Join(keystore, keys[0].Name())
  }
docs: // PeerUserKey returns the path to the private key for the specified user in
  // the peer organization.