User.UserMembershipData

Type: object
Object Properties
destinyMemberships
this allows you to see destiny memberships that are visible and linked to this account (regardless of whether or not they have characters on the world server)
Type: array
Array Contents: GroupsV2.GroupUserInfoCard
primaryMembershipId
Nullable
If this property is populated, it will have the membership ID of the account considered to be "primary" in this user's cross save relationship.

If null, this user has no cross save relationship, nor primary account.
Type: int64
bungieNetUser