code: func (actor Actor) GrantSpaceManagerByUsername(orgGUID string, spaceGUID string, username string) (Warnings, error) {
  	if actor.Config.UAAGrantType() == string(uaaconst.GrantTypeClientCredentials) {
  		return actor.grantSpaceManagerByClientCredentials(orgGUID, spaceGUID, username)
  	}
  
  	return actor.grantSpaceManagerByUsername(orgGUID, spaceGUID, username)
  }
docs: // GrantSpaceManagerByUsername makes the provided user a Space Manager in the
  // space with the provided guid.