Add RFC THV-0020 for header injection in remote MCP proxies #26
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JAORMX
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Jan 22, 2026
This RFC proposes server-side configuration for injecting HTTP headers into requests forwarded to remote MCP servers. Currently, if specific headers need to be sent to remote servers, clients must configure them individually, which is brittle and doesn't scale across different MCP client implementations. The solution uses a middleware that injects configured header name-value pairs into every request, following the existing token_injection pattern. This provides a single, centralized configuration point for operators. Affected components: - thv proxy command (--remote-forward-headers flag) - thv run command for remote URLs (--remote-forward-headers flag) - MCPRemoteProxy Kubernetes CRD (headerForward.addHeaders field) Related: stacklok/toolhive#3316
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@JAORMX I added a new section that focuses on adding headers with potentially secret value, wdyt? |
JAORMX
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Jan 23, 2026
…nflict detection - Add restricted header blocklist (hop-by-hop, identity-spoofing, smuggling vectors) - Add configuration-time validation for token exchange/injection conflicts - Update middleware signature to return error on restricted headers - Update Security Considerations with new mitigations
JAORMX
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Jan 23, 2026
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This RFC proposes server-side configuration for injecting HTTP headers into requests forwarded to remote MCP servers. Currently, if specific headers need to be sent to remote servers, clients must configure them individually, which is brittle and doesn't scale across different MCP client implementations.
The solution uses a middleware that injects configured header name-value pairs into every request, following the existing token_injection pattern. This provides a single, centralized configuration point for operators.
Affected components:
Related: stacklok/toolhive#3316