That can be done with an email and an email confirmation from all parts.
What is in the contract should be a wide range of rights and duties that people commonly fulfill with marriage, all parties involved must opt in to the ones they want to be protected by that contract.
Starting by writing a letter to the asgardian government listing all emails that will be in the contract.
That can be done from a webpage.
In that message they ask for the official link to be sent to those emails, so that if a person is not asgardian can recieve a link to fallow asgrardian citizenship procedures.
Once that procedure is done, the email is in the database but the person is not yet asgardian, they will just be able to continue.
Then they can independently opt in on the rights and duties they want and recieve an email explaining which are the things they didn't chose commonly. That can give a broader spectrum of the relationship.
Finally they are asked if they want to opt in to those things they didn't choose, they can press all or just the ones they want, it's up to them how many times it goes back and forward, once they agree, boom it's done.
They are in the system, their confirmation is sent and they can recieve an official Asgardian certification of union and the contract for a fee.
That fee goes to the asgardian government.
And is a wonderful thing they can both display wherever they are.
They should be able to choose the language they want the certificate, the template and the quantity of copies separately and pay separately, other things could be added.
It is important to provide security, so that contracts have to be renewed after a cool down period to ensure a healthy relationship and a sense of responsibility before and after.
People should be free to chose who they want to be in a relationship with asgardian, earthling, alien, it's all good if they can use an email.
Legal age should be open to discussion.
There's no need to limit how many are in the relationship or what gender they are. But there can only be one contract, with full names.
Thats my idea for a civil union agreement as things are today.
Inputs and feedback is welcome.
Have a nice day.