Entra External ID for customer access

For customer-facing portals built on Power Pages — or any scenario where external users need to authenticate to access Dynamics 365 resources — the identity provider is Microsoft Entra External ID. Successor to Azure AD B2C, External ID provides customer-grade identity: branded sign-up flows, social identity, MFA, and the scale to handle millions of consumer users without overloading the workforce-focused Microsoft Entra ID directory.

The model.

External ID is a separate tenant from your workforce Entra ID:

• Workforce tenant — employees, contractors, internal users. The standard Microsoft 365 / Entra ID directory.
• External tenant — customers, partners, citizens. Separated for isolation, scale, and customer-grade flows.

Users in the external tenant don't have Microsoft 365 licenses, internal access, or workforce identity overhead. They exist purely as external identities for accessing customer-facing resources.

Identity providers

External ID accepts identity from multiple sources:

• Email / password — locally-managed accounts.
• Microsoft account — using a personal Microsoft account.
• Google, Facebook, Apple, LinkedIn, Twitter — social identity providers.
• Any OpenID Connect / SAML 2.0 provider — for federated identity from a partner organisation.

Customers sign up with whichever identity works for them; the External ID maintains a unified user record.

User flows

A user flow is a configured authentication / registration experience:

• Sign-up and sign-in flow — the most common; users register or sign in.
• Sign-up only — for registration-only scenarios.
• Password reset — self-service password reset.
• Profile editing — let users update their own data.

Each flow has configurable steps — attributes to collect, MFA requirements, consent screens, branding.

Branding

External ID supports per-application branding:

• Custom logo and colours.
• Custom HTML pages for sign-in / sign-up.
• Multi-language support.
• Custom domain (e.g. auth.contoso.com) instead of the Microsoft-default URL.

Customers see a branded experience that feels like part of your product, not a Microsoft service.

MFA

Configurable per user flow:

• Always required — high-security scenarios.
• Conditional — based on risk signals, location, sensitive operations.
• Optional — user can enable.

MFA methods include SMS, email OTP, authenticator apps.

Custom attributes

Beyond standard attributes (email, name), define custom attributes for capture at sign-up:

• Company name.
• Customer reference number.
• Region / language.
• Communication preferences.
• Custom JSON for complex data.

Stored on the External ID user; flows back to the integrated systems (Power Pages, Dataverse) on authentication.

Custom policies

For advanced scenarios beyond user-flow capability, External ID supports custom policies — XML-based identity orchestration that can include:

• Multi-step verification (email + phone + ID document).
• Integration with external identity verification services.
• Complex conditional logic.
• Custom claims transformation.

Custom policies are powerful but complex; reserve for genuine business needs.

Integration with Power Pages

Power Pages portals can use External ID as their identity provider:

1. In the Power Pages site settings, configure External ID as an authentication provider.
2. Map the External ID flow to portal sign-in / sign-up paths.
3. Map External ID attributes to Power Pages contact records (Dataverse).
4. Portal authenticated sessions get Dataverse-side identity automatically.

The pattern: customer signs up through External ID; their record creates / matches a Contact in Dataverse; they get portal access scoped to their data.

Migration from Azure AD B2C.

External ID is the modern successor to Azure AD B2C. Microsoft has signaled long-term migration paths:

• B2C tenants continue running.
• New external-identity scenarios should target External ID.
• Migration tools assist moving B2C user populations to External ID.

For existing B2C-based Power Pages or custom-app deployments, gradual migration over months is the typical path.

Pricing

External ID is billed by monthly active user (MAU) — the number of unique external users authenticating in the month. Tiers offer different feature levels; sized per expected user scale.

Security and compliance.

• GDPR compliance — External ID handles customer PII with appropriate controls.
• Audit logs — sign-in events, profile changes, MFA events.
• Conditional Access — apply policies based on risk signals.
• Identity Protection — Microsoft detects unusual sign-in patterns.

Common pitfalls.

• B2C used where External ID would suit — older docs still reference B2C; for new builds, prefer External ID.
• Branding skipped — users see "Sign in with Microsoft" branding; jarring.
• No MFA on customer access — increases account-takeover risk.
• Attribute structure not thought through — adding attributes after launch is more friction than getting them right upfront.

Operational reality

External ID is the canonical answer for customer-facing identity in the Microsoft cloud. Plan for it deliberately; treat it as production infrastructure; tune branding and flows based on user feedback.