[Dcastroro]

HTTP/SSE connections currently support a custom Authorization header but cannot send other server-specific headers. mcp tools https://example.com/mcp --headers X-Project=demo leaves --headers in the server arguments, so the URL is treated as a stdio command instead of an HTTP endpoint.

Add repeatable --headers NAME=VALUE options for the list commands and call. Header names are case-insensitive (last value wins), values can contain =, and explicit authentication options retain precedence. Invalid names/control characters fail before connecting, with errors that omit the supplied value.

When custom headers are configured, an HTTP transport wrapper applies them to every same-origin request, including Streamable HTTP session teardown. It rejects requests to another scheme, host or port before sending them; this covers both redirects and SSE message endpoints. Same-origin redirects continue to work. Connections without custom headers retain their existing transport behavior.

Fixes #81.

Validation on Ubuntu 24.04 / Go 1.24.1:

• Parser regressions fail on unchanged main: custom headers are left in the stdio command arguments.
• Full go test -race -json ./... passes. Tests exercise real local HTTP and SSE MCP servers, repeated headers, embedded =, empty values, authentication precedence and malformed header rejection.
• Local HTTP tests verify that a cross-origin redirect/direct request does not reach the other server and that a scheme change is rejected. No external services or real credentials are used.
• golangci-lint run --timeout=5m ./... (v2.0.2): zero issues; the existing unknown shadow nolint warning remains.
• README includes examples using non-sensitive project/mode headers. No dependency changes.

Reviewed the 15 open PRs and issue timeline before preparing the change. #94 loads server configurations and explicitly leaves SSE headers unsupported; it does not implement this option. This branch is based on upstream master independently of #98 (argument separator support).

[Copilot]

🔵 Needs a closer look

The change introduces security-sensitive networking logic (a custom RoundTripper enforcing same-origin header delivery, redirect handling, and header-injection validation) where subtle correctness matters, so final human review is warranted.

0 open findings

What changed in this PR

This PR implements custom HTTP header support for HTTP (Streamable) and SSE MCP connections, resolving #81. Previously only an Authorization header could be set; other server-specific headers were impossible, and --headers was incorrectly left in the server arguments (causing the URL to be treated as a stdio command). The change adds a repeatable --headers NAME=VALUE option and routes custom headers through an origin-restricted HTTP transport wrapper.

Changes:

• Add a repeatable --headers NAME=VALUE flag parsed by ProcessFlags (list commands) and parseCallArgs (call), with RFC 7230 token/control-character validation that fails before connecting and never echoes the supplied value.
• When custom headers are present, wrap the transport's HTTP client with a RoundTripper that re-applies headers on every same-origin request and rejects any scheme/host/port change (covering redirects and SSE message endpoints); explicit --auth-user/--auth-header retain precedence over a custom Authorization.
• Add unit/integration tests against real local HTTP and SSE servers plus README documentation.

File	Description
cmd/​mcptools/​commands/​http_headers.go	New header validation, origin-restricted RoundTripper, and client wrapper.
cmd/​mcptools/​commands/​utils.go	Applies custom headers in CreateClientFunc, wires the wrapper into SSE/HTTP transports, and parses --headers in ProcessFlags.
cmd/​mcptools/​commands/​root.go	Adds the FlagHeaders constant, CustomHTTPHeaders global, and persistent --headers flag registration.
cmd/​mcptools/​commands/​call.go	Parses --headers within parseCallArgs.
cmd/​mcptools/​commands/​http_headers_test.go	Tests parsing, validation/injection rejection, transport behavior, and origin enforcement.
README.md	Documents the --headers option, precedence, and origin restrictions.

🧠 Review effort: Balanced

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