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auth: allow passing custom http.Client to AuthorizationCodeHandler (#840)

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Maciej Kisiel 2026-03-13 10:06:58 +01:00 • committed by GitHub
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@ -13,6 +13,7 @@
1. [Security](#security)
1. [Confused Deputy](#confused-deputy)
1. [Token Passthrough](#token-passthrough)
1. [Server-Side Request Forgery (SSRF)](#server-side-request-forgery-(ssrf))
1. [Session Hijacking](#session-hijacking)
1. [Utilities](#utilities)
1. [Cancellation](#cancellation)
@ -363,7 +364,7 @@ the MCP spec's [Security Best Practices](https://modelcontextprotocol.io/specifi
### Confused Deputy
The [mitigation](https://modelcontextprotocol.io/specification/2025-06-18/basic/security_best_practices#mitigation),
The [mitigation](https://modelcontextprotocol.io/docs/tutorials/security/security_best_practices#mitigation),
obtaining user consent for dynamically registered clients, is mostly the
responsibility of the MCP Proxy server implementation. The SDK client does
generate cryptographically secure random `state` values for each authorization
@ -372,15 +373,36 @@ Mismatched state values will result in an error.
### Token Passthrough
The [mitigation](https://modelcontextprotocol.io/specification/2025-06-18/basic/security_best_practices#mitigation-2), accepting only tokens that were issued for the server, depends on the structure
The [mitigation](https://modelcontextprotocol.io/docs/tutorials/security/security_best_practices#mitigation-2), accepting only tokens that were issued for the server, depends on the structure
of tokens and is the responsibility of the
[`TokenVerifier`](https://pkg.go.dev/github.com/modelcontextprotocol/go-sdk/auth#TokenVerifier)
provided to
[`RequireBearerToken`](https://pkg.go.dev/github.com/modelcontextprotocol/go-sdk/auth#RequireBearerToken).
### Server-Side Request Forgery (SSRF)
The [mitigations](https://modelcontextprotocol.io/docs/tutorials/security/security_best_practices#mitigation-3) are as follows:
- _Enforce HTTPS_. The OAuth helpers provided by the SDK reject the `http://` URLs
except loopback addresses (`localhost`, `127.0.0.1`, `::1`).
- _Block Private IP Ranges_. The OAuth helpers provided by the SDK allow passing
a custom `http.Client`. Developers are advised to customize the client it with
appropriate network protections, including IP range blocking. The SDK does not provide
this capability out of the box.
- _Validate Redirect Targets_. Similarly to previous point, customized `http.Client`
can be used to validate network hops. The SDK does not provide this capability out
of the box.
- _Use Egress Proxies_. This is out of scope for the SDK and can be configured separately.
- _DNS Resolution Considerations_. The SDK has DNS rebinding protection on the server side which is enabled by default. For the client side, consider providing
a custom `http.Client` that would implement DNS pinning.
### Session Hijacking
The [mitigations](https://modelcontextprotocol.io/specification/2025-06-18/basic/security_best_practices#mitigation-3) are as follows:
The [mitigations](https://modelcontextprotocol.io/docs/tutorials/security/security_best_practices#mitigation-4) are as follows:
- _Verify all inbound requests_. The [`RequireBearerToken`](https://pkg.go.dev/github.com/modelcontextprotocol/go-sdk/auth#RequireBearerToken)
middleware function will verify all HTTP requests that it receives. It is the