saml.xml

<saml2:Attribute Name="groups" NameFormat="urn:oasis:names:tc:SAML:2.0:attrname-format:unspecified"> 
  <saml2:AttributeValue 
                        xmlns:xs="http://www.w3.org/2001/XMLSchema" 
                        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
                        xsi:type="xs:string">
    fed_member_of_fishing_accounting
  </saml2:AttributeValue> 
  <saml2:AttributeValue 
                        xmlns:xs="http://www.w3.org/2001/XMLSchema"
                        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
                        xsi:type="xs:string">
    fed_member_of_all_projects
  </saml2:AttributeValue>
</saml2:Attribute>

[root@pike-aio ~(keystone_admin)]# cat rules.test
MELLON_email: me@you.com
MELLON_groups: test1;test2;test3
[root@pike-aio ~(keystone_admin)]# keystone-manage mapping_engine --rules rules.json --input rules.test
{
  "group_ids": [],
  "user": {
    "domain": {
      "id": "Federated"
    },
    "type": "ephemeral",
    "name": "me@you.com"
  },
  "projects": [],
  "group_names": [
    {
      "domain": {
        "name": "Default"
      },
      "name": "['test1', 'test2', 'test3']"
    }
  ]
}