As a user of Programs or Instances, I can specify a custom domain for my VM

[hoh]

• The message must contain the custom domain of the user.
• The ownership of the domain is validated by a TXT record containing the user's address
• The user must configure a CNAME pointing to aleph.im's DNS servers or a copy

[MHHukiewitz]

Can now be done using

• the SDK: Feature : AlephDNS (2nd attempt) aleph-sdk-python#55
• and the client: Feature: add custom domain support aleph-client#167