According to the Alur law, as a landlord, you can subscribe on behalf of your tenant on the sole condition that he cannot do it himself (defaulting tenant). 

Default is defined in the law. For more information, refer to the law. 

⚠ A very strict procedure in this law must be followed. 

In the case of co-tenancy, if you are a landlord, you can provide for this possibility in the lease (the procedure is also described in the Alur law).