Feature Request: Support HTTP Authorization headers for direct CLI usage

🤖 *Written by Claude Code*

---

## Summary

Add support for passing HTTP Authorization headers when using `mcptools` CLI commands (`tools`, `call`, `shell`) with HTTP/SSE MCP servers that require authentication.

## Use Case

Many MCP servers (like [Linear's MCP server](https://linear.app/docs/mcp)) require Bearer token authentication. Currently, there's no way to pass these headers when using mcptools directly from the command line.

**Example scenario:**
```bash
# This should work but doesn't - no way to pass auth headers
mcptools tools https://mcp.linear.app/mcp --headers "Authorization=Bearer "
```

## What Was Tried

### Attempt 1: Direct URL with --headers flag
```bash
mcptools tools https://mcp.linear.app/mcp --headers "Authorization=Bearer "
```
**Result:** `--headers` flag is not recognized for `tools` command.

### Attempt 2: Adding headers to aliases.json
```bash
mcptools alias add linear https://mcp.linear.app/mcp
```
Then manually edited `~/.mcpt/aliases.json`:
```json
{
"linear": {
"command": "https://mcp.linear.app/mcp",
"headers": {
"Authorization": "Bearer "
}
}
}
```
```bash
mcptools tools linear
```
**Result:** `401 Unauthorized` - the headers field in aliases.json is not being read/sent.

### Attempt 3: Environment variable
```bash
MCP_HTTP_HEADERS="Authorization=Bearer " mcptools tools https://mcp.linear.app/mcp
```
**Result:** `401 Unauthorized` - environment variable not recognized.

### Attempt 4: Using configs set (partial success)
```bash
mcptools configs set mcp-linear linear https://mcp.linear.app/mcp \
--config ~/.mcpt/mcp-config.json \
--headers "Authorization=Bearer "
```
**Result:** Successfully stores the config with headers visible in `configs view`:
```
mcp-linear
linear (sse):
https://mcp.linear.app/mcp
Authorization: Bearer
```
BUT there's no way to use this config with `tools`/`call`/`shell` commands:
```bash
mcptools tools mcp-linear:linear
# Error: executable file not found in $PATH
```

## Analysis

The `configs` subsystem appears designed for managing IDE config files (Cursor, VSCode, Windsurf), not for direct mcptools CLI usage. The HTTP transport code auto-detects URLs but has no mechanism to accept custom headers.

## Suggested Solutions

### Option A: Add --headers flag to relevant commands
```bash
mcptools tools https://mcp.linear.app/mcp --headers "Authorization=Bearer "
mcptools call https://mcp.linear.app/mcp list_issues --headers "Authorization=Bearer "
mcptools shell https://mcp.linear.app/mcp --headers "Authorization=Bearer "
```

### Option B: Support headers in aliases.json
Make the alias system read and use the `headers` field for HTTP URLs:
```json
{
"linear": {
"command": "https://mcp.linear.app/mcp",
"headers": {
"Authorization": "Bearer "
}
}
}
```
Then `mcptools tools linear` would send those headers.

### Option C: Environment variable support
```bash
MCP_HTTP_HEADERS="Authorization=Bearer " mcptools tools https://mcp.linear.app/mcp
# or
MCP_AUTH_TOKEN="" mcptools tools https://mcp.linear.app/mcp
```

### Option D: Use configs for direct CLI usage
Allow referencing servers from config aliases:
```bash
mcptools tools --config mcp-linear --server linear
# or
mcptools tools @mcp-linear:linear
```

## Real-World Impact

This would enable CLI usage of:
- [Linear MCP](https://mcp.linear.app/mcp) - project management
- [Slack MCP](https://slack.com) - team communication
- Any OAuth-protected MCP server
- Enterprise MCP servers with API key authentication

## Environment

- OS: Linux (Arch)
- mcptools version: latest (installed via `go install`)
- MCP server tested: `https://mcp.linear.app/mcp`

## Related

- Linear MCP docs: https://linear.app/docs/mcp
- MCP OAuth spec: https://modelcontextprotocol.io/specification/draft/basic/authorization

Thank you for this excellent tool! Adding header support would make it complete for HTTP-based MCP servers.