mcp: add mcp method and tool logging to authorize (#5668)

## Summary

Adds support for extending authorization log with Model Context Protocol
details.

i.e. 
```json
{
  "level": "info",
  "server-name": "all",
  "service": "authorize",
  "mcp-method": "tools/call",
  "mcp-tool": "describe_table",
  "mcp-tool-parameters": { "table_name": "Categories" },
  "allow": true,
  "allow-why-true": ["email-ok", "mcp-tool-ok"],
  "deny": false,
  "deny-why-false": [],
  "time": "2025-06-24T17:40:41-04:00",
  "message": "authorize check"
}
```

## Related issues

Fixes
https://linear.app/pomerium/issue/ENG-2393/mcp-authorize-each-incoming-request-to-an-mcp-route

## User Explanation

<!-- How would you explain this change to the user? If this
change doesn't create any user-facing changes, you can leave
this blank. If filled out, add the `docs` label -->

## Checklist

- [x] reference any related issues
- [x] updated unit tests
- [x] add appropriate label (`enhancement`, `bug`, `breaking`,
`dependencies`, `ci`)
- [x] ready for review

authorize/evaluator/evaluator.go

@@ -4,7 +4,6 @@ package evaluator
 import (
 	"context"
 	"encoding/base64"
-	"encoding/json"
 	"encoding/pem"
 	"fmt"
 	"net/http"
@@ -135,12 +134,6 @@ type RequestSession struct {
 	ID string `json:"id"`
 }
 
-// RequestMCP is the MCP field in the request.
-type RequestMCP struct {
-	Tool   string `json:"tool,omitempty"`
-	Method string `json:"method,omitempty"`
-}
-
 // Result is the result of evaluation.
 type Result struct {
 	Allow               RuleResult
@@ -477,36 +470,3 @@ func carryOverJWTAssertion(dst http.Header, src map[string]string) {
 		dst.Add(jwtForKey, jwtFor)
 	}
 }
-
-// RequestMCPFromCheckRequest populates a RequestMCP from an Envoy CheckRequest proto for MCP routes.
-func RequestMCPFromCheckRequest(
-	in *envoy_service_auth_v3.CheckRequest,
-) (RequestMCP, bool) {
-	var mcpReq RequestMCP
-
-	body := in.GetAttributes().GetRequest().GetHttp().GetBody()
-	if body == "" {
-		return mcpReq, false
-	}
-
-	var jsonRPCReq struct {
-		Method string         `json:"method"`
-		Params map[string]any `json:"params,omitempty"`
-	}
-
-	if err := json.Unmarshal([]byte(body), &jsonRPCReq); err != nil {
-		return mcpReq, false
-	}
-
-	mcpReq.Method = jsonRPCReq.Method
-
-	if jsonRPCReq.Method == "tools/call" {
-		if name, exists := jsonRPCReq.Params["name"]; exists {
-			if toolName, ok := name.(string); ok {
-				mcpReq.Tool = toolName
-			}
-		}
-	}
-
-	return mcpReq, true
-}