identity-membership

Identity, User, Membership

A person who signs in is an Identity. A workspace they can enter is a Tenant (or Account). The join is Membership. Sessions hang on Identity, never on the tenant-scoped User.

This sits on top of magic-link-auth. In SQLite-per-tenant apps it also sits on activerecord-tenanted. Fizzy uses the same split in a single database.

Philosophy

Identity authenticates. Membership authorizes. User is the in-tenant person. Mixing these is how you leak one customer's users into another shard.
One email, many workspaces. Don't create a second Identity when someone joins a second tenant.
Create Membership globally, then the tenanted User inside with_tenant. Order matters; a User without a Membership is an orphan.
Join codes are shareable, not emailed magic links. Different secret, different table.

The records

Identity  (global)  email, sessions, magic links, access tokens
   │
   ├── Membership (global)  identity_id + tenant_id + role
   │
   └── User (tenanted, Cortex/Innkeeper)  identity_id + name + in-tenant role

Herald skips the tenanted User: AccountMembership on the global DB is enough because account members can see every project. Cortex/Innkeeper need a User inside the tenant DB for project assignments, comments, and audit actor.

Fizzy's User is the membership row in the same database (users.identity_id + account_id). Same idea, no shard.

Step 1: Identity stays global

class Identity < GlobalRecord
  has_many :sessions, dependent: :destroy
  has_many :magic_links, dependent: :destroy
  has_many :memberships, dependent: :destroy
  has_many :tenants, through: :memberships

  validates :email, presence: true, uniqueness: { case_sensitive: false }
  normalizes :email, with: ->(email) { email.downcase.strip }
end

Sign-in creates a Session for this Identity (magic-link-auth). It does not pick a tenant.

Step 2: Membership is the join

class Membership < GlobalRecord
  belongs_to :identity
  belongs_to :tenant  # or :account

  enum :role, { admin: "admin", member: "member" }, default: :member
  validates :identity_id, uniqueness: { scope: :tenant_id }
end

Roles live here for "can they enter this workspace at all." Finer ACL (board access, project assignments) lives on tenanted records.

Herald: AccountMembership with owner / member. Innkeeper adds viewer.

Step 3: Tenanted User (when the workspace has a person record)

class User < ApplicationRecord
  validates :identity_id, presence: true, uniqueness: true
  enum :role, { admin: "admin", member: "member" }

  def identity
    Identity.find_by(id: identity_id)
  end
end

No FK to identities — different database. Copy role from Membership at join time; don't treat the two roles as independent sources of truth.

Step 4: Join in one method

def join(tenant, name: nil, role: :member)
  was_new = false

  GlobalRecord.transaction do
    membership = memberships.find_or_create_by!(tenant: tenant) do |record|
      record.role = role
      was_new = true
    end

    ApplicationRecord.with_tenant(tenant.external_id) do
      User.find_or_create_by!(identity_id: id) do |user|
        user.role = membership.role
        user.name = name || email.split("@").first.titleize
      end
    end
  end

  was_new
end

Rescue RecordNotUnique and re-find — two tabs will race. Herald's Account#add_member! is the same idea without a tenanted User.

After magic-link verify, if identity.tenants.none?, send them to create-tenant / new-project. If they have tenants, send them to the last one or a picker.

Step 5: Current

# After cookie auth (global):
Current.identity = session.identity

# After TenantScoping:
Current.tenant = tenant
Current.user = User.find_by(identity_id: Current.identity.id)

def require_membership!
  redirect_to sign_in_path unless Current.user
end

Current.user is nil when the Identity is signed in but has no Membership in this tenant. That's a 403, not a sign-in loop.

Don't set Current.user from the session. The session doesn't know which tenant the URL selected.

Step 6: Join codes

Shareable XXXX-XXXX-XXXX (Base58, no 0/O/I/l). Global table. One active code per tenant/project.

class JoinCode < GlobalRecord
  belongs_to :tenant  # or :project / :account

  def redeem_if
    with_lock do
      increment!(:usage_count) if active? && yield
    end
  end
end

Redeem:

Load JoinCode by code (global).
If not signed in, stash the code in the session and send them through magic-link.
identity.join(tenant) then redeem_if.
Rate-limit the redeem endpoint.

Don't use a magic-link code as an invite. Don't increment usage until join succeeds.

Anti-Patterns

has_many :sessions on User — logout/login is per person, not per workspace.
find_or_create_by(email:) inside a tenant — creates duplicate people; Identity is the uniqueness boundary.
Authorizing with Current.identity only — they might not be a member of this tenant.
Creating User before Membership — User in a shard with no global join row.
Nebula Member on workspace — different tenancy; don't copy that into an activerecord-tenanted app.
Emailing the join code in the magic-link mailer — two flows, two templates.

Sign-in codes and session cookies: magic-link-auth
Shard switching: activerecord-tenanted

See reference.md for Herald vs Cortex/Innkeeper vs Fizzy, and test helpers.

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