[FR] Allow MCP client to pass non sb auth token in request.

[KonradStanski]

In some cases where sb is run in no-auth mode, auth is implemented by a reverse proxy such as dex or google auth infront of the API.
It would be usefull to provide a mechanism for the MCP client to auth with these other methods, by passing a auth bearer token.

Claude writeup of a potential fix:

Sourcebot MCP Server - Dex/Bearer Token Authentication Support

================================================================

This document describes the changes needed to add Bearer token

authentication support to @sourcebot/mcp for use with Dex or

other OAuth2/OIDC providers.

Overview

Currently the MCP server only supports SOURCEBOT_API_KEY which sets
the X-Sourcebot-Api-Key header. To work with Dex, we need to add
support for Bearer tokens via the Authorization: Bearer <token> header.

Files to Modify/Create

1. packages/mcp/src/env.ts - Add new environment variables
2. packages/mcp/src/auth.ts - New file for centralized auth logic
3. packages/mcp/src/client.ts - Use the new auth module

================================================================================

1. env.ts - Add these environment variables

================================================================================

Add after the existing SOURCEBOT_API_KEY definition:

// Bearer token auth (for Dex, OAuth2, OIDC)
SOURCEBOT_AUTH_TOKEN: z.string().optional(),

// Auth type selector: 'api-key' | 'bearer' | 'auto'
// 'auto' will prefer bearer token if set, then api-key
SOURCEBOT_AUTH_TYPE: z.enum(['api-key', 'bearer', 'auto']).default('auto'),

================================================================================

2. auth.ts - Create new file

================================================================================

Create packages/mcp/src/auth.ts:

import { env } from './env.js';

export type AuthHeaders = Record<string, string>;

/**
 * Builds authentication headers based on configured auth method.
 *
 * Priority (when SOURCEBOT_AUTH_TYPE is 'auto'):
 * 1. Bearer token (SOURCEBOT_AUTH_TOKEN) - for Dex/OAuth2/OIDC
 * 2. API key (SOURCEBOT_API_KEY) - for Sourcebot native auth
 * 3. No auth headers
 */
export const getAuthHeaders = (): AuthHeaders => {
    const authType = env.SOURCEBOT_AUTH_TYPE;

    // Bearer token auth
    if (authType === 'bearer') {
        if (!env.SOURCEBOT_AUTH_TOKEN) {
            throw new Error(
                'SOURCEBOT_AUTH_TOKEN required when SOURCEBOT_AUTH_TYPE is "bearer"'
            );
        }
        return { 'Authorization': `Bearer ${env.SOURCEBOT_AUTH_TOKEN}` };
    }

    // API key auth
    if (authType === 'api-key') {
        if (!env.SOURCEBOT_API_KEY) {
            throw new Error(
                'SOURCEBOT_API_KEY required when SOURCEBOT_AUTH_TYPE is "api-key"'
            );
        }
        return { 'X-Sourcebot-Api-Key': env.SOURCEBOT_API_KEY };
    }

    // Auto-detect: prefer bearer, then api-key
    if (env.SOURCEBOT_AUTH_TOKEN) {
        return { 'Authorization': `Bearer ${env.SOURCEBOT_AUTH_TOKEN}` };
    }
    if (env.SOURCEBOT_API_KEY) {
        return { 'X-Sourcebot-Api-Key': env.SOURCEBOT_API_KEY };
    }

    return {};
};

================================================================================

3. client.ts - Update to use auth module

================================================================================

Add import at top:

import { getAuthHeaders } from './auth.js';

Replace all instances of:

... (186 lines left)