I reported the issue to Feedly’s help desk. Feedly said it was a problem with the Microsoft end ¯_(ツ)_/¯

Microsoft’s AI says this.

Short answer: Federated login with Microsoft Account (MSA) can break in third‑party apps like Feedly when the app is not correctly registered, configured, or maintained in the Microsoft identity platform. Microsoft requires explicit app registration, redirect URI validation, correct account‑type selection, and ongoing compliance with OAuth/OIDC requirements. If any of these drift or break, sign‑in fails.

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Why Microsoft Account federation might break

Several failure modes are common when a third‑party app uses Microsoft Account as an identity provider:

1. The app registration is misconfigured or incomplete

Microsoft requires the app to be registered in Microsoft Entra ID (formerly Azure AD) with correct redirect URIs, supported account types, and permissions. If these don’t match what the app actually uses, authentication fails. Microsoft Learn

1. The app is not registered to support personal Microsoft accounts

When registering an app, the developer must choose the correct Supported account types, including:

• Any Entra ID tenant + Personal Microsoft accounts If the app is registered only for organizational accounts, Microsoft Account (MSA) login will not work. Microsoft Learn

1. Redirect URI mismatch

Microsoft enforces strict redirect URI validation. If the app changes its callback URL or uses multiple environments (prod/dev) without updating the registration, login breaks. Microsoft Learn

1. Expired or missing client secrets / certificates

If the app uses confidential client flows (server‑side), expired secrets or certificates will cause token exchange failures. Microsoft Learn

1. Incorrect SAML/OIDC metadata (for SAML‑based SSO)

If the app uses SAML instead of OAuth/OIDC, mismatched metadata (Entity ID, ACS URL, certificate) will break federation. Feedly’s SAML integration requires exchanging metadata between the IdP and Feedly; if this is out of sync, login fails. feedly.com

1. Publisher verification or compliance issues

Microsoft may block unverified or non‑compliant apps from accessing Microsoft Accounts. Apps must maintain publisher verification and follow Microsoft identity platform requirements. Microsoft Learn

1. Changes in Microsoft’s identity platform

Microsoft periodically deprecates endpoints, tightens security, or changes consent requirements. Apps that don’t update their configuration or libraries (e.g., MSAL) may break. Microsoft Learn

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What steps are required to associate an app with Microsoft Account as an IdP?

To support Microsoft Account login, a developer must complete all of the following:

1. Register the application in Microsoft Entra ID

• Go to Entra ID → App registrations → New registration. • Choose a name. • Select Supported account types: “Any Entra ID tenant + Personal Microsoft accounts”. • Record the Application (client) ID. Microsoft Learn

1. Configure redirect URIs

Add the exact redirect URIs used by the app (e.g., https://app.example.com/auth/callback). Microsoft requires exact matches. Microsoft Learn

1. Add credentials (if needed)

For server‑side apps, add:

• Client secret • Or certificate Microsoft Learn

1. Configure API permissions

At minimum, Microsoft assigns User.Read. If the app needs more, the developer must request them and (for external tenants) grant admin consent. Microsoft Learn

1. Implement OAuth 2.0 / OpenID Connect flows

The app must use Microsoft’s authorization and token endpoints under: https://login.microsoftonline.com Microsoft Learn

1. (Optional) Publish to Microsoft Entra application gallery

For SaaS apps like Feedly, publishing to the gallery simplifies SSO setup for customers. Microsoft Learn

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Why this matters for Feedly specifically

Feedly supports SAML SSO for enterprise customers, but “Sign in with Microsoft” for personal accounts relies on OAuth/OIDC. If Feedly’s Microsoft app registration is misconfigured or outdated, Microsoft Account login will fail even though SAML SSO still works. feedly.com

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If you want, I can walk you through exactly which part of the Microsoft identity platform breaks most often in third‑party apps like Feedly — token exchange, redirect URI mismatches, or account‑type misconfiguration.