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Use WordPress Multisite when the sites can share one installation, shared user records, and common administration. Keep separate installations and connect their user tables only when database-level coupling is acceptable. Choose SAML single sign-on (SSO) when each site must keep its own database but users should authenticate once. User-sync plugins handle account provisioning; they do not make site content or permissions identical.
Three different problems: identity, access and login sessions
“Sharing users” can mean several things. A shared user record answers who the person is. A role or membership on a particular site answers what that person may do there. Single sign-on answers whether the person must enter credentials again when moving to another domain. Provisioning tools answer whether an account is created or removed on multiple sites.
Pick the architecture according to the boundary you need:
| Approach | Installation and data boundary | Login behavior | Role model | Best fit | Main trade-off |
|---|---|---|---|---|---|
| WordPress Multisite | One WordPress installation; sites have separate content tables and share the user table. | Network users use the same WordPress identity, with site access assigned separately. | Roles are granted per site. | One organization managing related sites. | Sites share the installation and its operational failure boundary. |
| Separate installations with shared tables | Independent WordPress installations read common user and, optionally, user-meta tables. | Each installation reads the same credentials, subject to compatible configuration. | Each site still controls its own capabilities and role assignments. | Separate codebases that must use one account store. | Backups, schema changes, password behavior and recovery become tightly coordinated. |
| SAML-style SSO | Each site keeps its own database; one site or service provides identity. | Authenticate at the identity provider, then move to service-provider sites without re-entering credentials. | Each service provider maps the incoming identity to local roles. | Strongly independent sites or different domains. | Certificates, metadata, attribute mapping, logout and provisioning require deliberate administration. |
| Synchronization plugins | Usually copies or provisions users between sites rather than merging databases. | Depends on the plugin; some also synchronize login sessions. | Often includes a default role or mapped role, but permissions remain site-specific. | Automating account creation or removal after choosing Multisite or separate sites. | Plugin compatibility, security and maintenance must be checked before deployment. |
When WordPress Multisite is the right answer
WordPress Developer Resources describes Multisite as several site instances managed within one installation. Each site has its own content tables, while the user table is shared. This is normally the simplest design when one team owns all sites and accepts shared administration, updates and hosting.
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What a shared user actually receives
A user created in the network’s common user tables is not automatically an administrator or editor everywhere. Add that user to each site they should enter, then assign the appropriate role in that site’s dashboard. A person can therefore be an administrator on one site, an editor on another and have no access to a third.
Operational consequences
- All sites depend on the same WordPress installation, database infrastructure and deployment process.
- Content remains separated by site tables, but network-level administration is shared.
- A network-wide change or outage can affect every site at once, so test updates and maintain a recovery plan for the whole network.
Use Multisite only when the boundaries fit
WordPress advises reconsidering a network when sites are strongly interconnected or need to share data or users in ways that require different boundaries. If teams, release schedules, security controls or ownership must remain independent, evaluate SSO instead.
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Separate installations with shared user tables
WordPress documentation for multiple instances describes pointing installations at common tables with the CUSTOM_USER_TABLE constant and, optionally, CUSTOM_USER_META_TABLE. When several sites use one database, distinct table prefixes can keep each site’s posts, settings and other tables separate while the user tables remain common.
What this design gives you
- Separate WordPress installations can retain different plugins, themes, deployment schedules and content databases.
- All installations can read one canonical set of user records instead of importing duplicate accounts.
- Site-level authorization still has to be configured so a shared identity is not mistaken for universal access.
Why it is tightly coupled
This is a database integration, not a loose login connection. Coordinate table schema changes, backups, restores, password updates and failure recovery across every installation. A restore that rolls back the shared user tables but not a site’s local metadata can leave accounts or role mappings inconsistent. Limit database write access carefully and test the arrangement on a staging copy before production.
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- Choose one canonical user and user-meta table and document its exact names.
- Configure every installation with the same
CUSTOM_USER_TABLEvalue; addCUSTOM_USER_META_TABLEonly if shared user metadata is required. - Use separate prefixes for each site’s non-user tables when the installations share a database.
- Verify account creation, password changes, email changes, role assignment and account deletion from each installation.
- Test backup and restore procedures with the shared tables included, then test one site’s recovery without overwriting another site’s content.
Use SAML SSO when the sites must remain independent
In a SAML arrangement, one WordPress site can act as the identity provider (IdP), while the other standalone sites act as service providers (SPs). A user signs in at the IdP; the SP sites trust the resulting assertion and establish local sessions, so the user does not type the password again on each domain.
What must be configured
- IdP and SP metadata, entity identifiers and assertion endpoints.
- Signing certificates and a process for rotating or revoking them.
- A stable identifier and attribute mapping, such as email or an immutable account ID.
- Local-user creation or linking rules and a mapping from incoming attributes to WordPress roles.
- Single logout expectations. Logging out of one site does not automatically prove that every other session has ended unless the SAML deployment supports and enforces that flow.
SSO is not user-table sharing
SAML transfers an authentication decision between systems; it does not merge their WordPress databases. Each site can keep its own users, content and permissions while trusting the IdP. Decide whether accounts are provisioned automatically, created on first login or maintained manually, and define what happens when an account is disabled at the IdP.
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Where synchronization plugins fit
Multisite provisioning tools
The WP Multisite User Sync/Unsync directory listing describes synchronizing or unsynchronizing users between sites in a Multisite network. It must be network activated and does not support a single standalone site. WPM User Sync describes automated synchronization and adding existing users to newly created sites with a default role.
These tools solve membership provisioning. They do not automatically synchronize posts, settings, plugin capabilities or every custom permission.
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Cross-site login tools
The Share Login listing describes synchronizing user logins between WordPress websites and providing single sign-on from a main site to a secondary site. Before relying on any such plugin, verify its current maintenance, supported WordPress and PHP versions, security design, data flow, logout behavior and commercial terms. A plugin that copies accounts is a different solution from one that brokers an authenticated session.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.A practical selection process
- List the boundaries. Record which sites share ownership, hosting, deployment, administrators and data. If those boundaries are genuinely common, Multisite may reduce complexity.
- Separate authentication from authorization. Decide whether you need one identity, one login session, automatic account creation, or all three. Do not grant a role merely because a user authenticated successfully.
- Choose the database model. Use Multisite for one installation; shared tables only when coordinated database operations are acceptable; SSO when databases must remain independent.
- Define lifecycle events. Document who can create, disable, rename and delete accounts, how role changes propagate, and how quickly access is revoked.
- Test the failure paths. Test an incorrect password, an unknown user, a disabled user, a missing role, an expired SAML certificate, an unavailable IdP and a restored database.
- Roll out gradually. Start with a test site and non-administrative accounts. Confirm login, logout, role mapping, password behavior, audit records and recovery before onboarding every domain.
Common mistakes to avoid
- Assuming a network user automatically has access to every site.
- Calling account copying “SSO” when users still authenticate separately at each site.
- Sharing user tables without a joint backup, schema and restore plan.
- Using a Multisite-only synchronization plugin with standalone installations.
- Mapping every SSO user to an administrator role instead of defining least-privilege mappings per site.
- Ignoring certificate rotation, account deprovisioning or logout behavior until after launch.
Recommended default
For a single organization operating closely related sites, start with Multisite and assign roles per site. For independent installations that only need one authentication authority, implement SAML SSO. Reserve shared user tables for teams prepared to operate a coupled database, and add synchronization plugins only for a clearly defined provisioning or login requirement.
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