基于Identity Server 4的外部提供商与刷新令牌登录流程问询

Hey there! Let's break down common technical questions and clarifications for this OAuth 2.0 + IdentityServer4 flow you've outlined:

First, let's recap your flow to align on context:

用户登录C时会被重定向至IS，在IS中选择EP并通过EP_code_grant方式登录，IS获取解析EP_access_token+EP_refresh_token后，生成IS_access_token+IS_refresh_token供用户访问C。

Key Questions & Practical Answers #

1. How does IdentityServer4 manage the external provider's tokens? #

• By default, IdentityServer4 stores the external provider (EP) access_token and refresh_token in its persisted grants store. This behavior is controlled by the SaveTokens flag when configuring the external provider in IS. You can retrieve these tokens later via the IProfileService or custom storage implementations using GetExternalTokensAsync.
• If you need to use EP tokens to call third-party APIs on the user's behalf later, ensure you enable token retention in your IS configuration.

2. What's the right way to handle refresh tokens for both IS and EP? #

• When client C uses its IS_refresh_token to request a new IS_access_token, IdentityServer4 can automatically refresh the EP_access_token (if the EP refresh token is still valid) without forcing the user to re-authenticate. This works out of the box if:
  • The external provider supports refresh tokens (not all do)
  • You configured the external provider in IS with scopes for offline access
• For client C, store the IS_refresh_token securely: use HttpOnly, SameSite, secure cookies for web apps, or platform-specific encrypted storage for native/mobile apps to prevent token theft.

3. How to customize claims from the external provider (EP) in IS? #

• Implement a custom IProfileService in IdentityServer4. In the GetProfileDataAsync method, you can fetch external claims from the user's identity, map them to your application's preferred claim types, and add custom claims before issuing the IS_access_token.
• Simplified example snippet:

  public async Task GetProfileDataAsync(ProfileDataRequestContext context)
  {
      // Filter out non-external claims
      var externalClaims = context.Subject.Claims
          .Where(c => c.Issuer != IdentityServerConstants.LocalIdentityProvider);
      
      // Your custom claim mapping logic
      var mappedClaims = MapExternalToInternalClaims(externalClaims);
      
      context.IssuedClaims.AddRange(mappedClaims);
  }
  

4. Critical security considerations to prioritize #

• Token Storage: Secure IS_refresh_token and EP_refresh_token at all times. For web clients, use HttpOnly/SameSite cookies with secure flags; for native apps, leverage platform secure storage APIs.
• Token Expiry & Rotation: Set short expiry times (15-30 mins) for IS_access_token, and enable refresh token rotation in IS to limit the impact of stolen tokens.
• External Provider Validation: Always verify the EP_access_token's signature and issuer before trusting its claims. IdentityServer4 does this by default for well-known providers, but double-check for custom providers.
• Client Authentication: Ensure hybrid client C authenticates with IS using a client secret or certificate when exchanging authorization codes for tokens, to block code theft attacks.

5. Troubleshooting tips for flow issues #

• Enable detailed logging in IdentityServer4 (set log level to Debug/Trace) to track request flows, token exchanges, and external provider errors.
• Use tools like Postman to simulate the authorization code flow between C, IS, and EP, isolating where failures occur (e.g., token exchange errors, claim mapping issues).
• Check the external provider's developer console for logs related to your app's requests.

内容的提问来源于stack exchange，提问作者Alexandre Costa