feat(15-01): add StackOverflow, Reddit, HackerNews recon sources

- StackOverflowSource searches SE API v2.3 search/excerpts endpoint
- RedditSource searches Reddit JSON API with custom User-Agent
- HackerNewsSource searches Algolia HN API for comments
- All credentialless, use ciLogKeyPattern for key detection
- Tests use httptest mock servers with API key patterns

pkg/recon/sources/stackoverflow.go

@@ -0,0 +1,112 @@
+package sources
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"time"
+
+	"golang.org/x/time/rate"
+
+	"github.com/salvacybersec/keyhunter/pkg/providers"
+	"github.com/salvacybersec/keyhunter/pkg/recon"
+)
+
+// StackOverflowSource searches Stack Exchange API for questions and answers
+// containing leaked API keys. Developers frequently paste credentials in
+// code examples when asking for help debugging API integrations.
+type StackOverflowSource struct {
+	BaseURL  string
+	Registry *providers.Registry
+	Limiters *recon.LimiterRegistry
+	Client   *Client
+}
+
+var _ recon.ReconSource = (*StackOverflowSource)(nil)
+
+func (s *StackOverflowSource) Name() string               { return "stackoverflow" }
+func (s *StackOverflowSource) RateLimit() rate.Limit       { return rate.Every(2 * time.Second) }
+func (s *StackOverflowSource) Burst() int                  { return 3 }
+func (s *StackOverflowSource) RespectsRobots() bool        { return false }
+func (s *StackOverflowSource) Enabled(_ recon.Config) bool { return true }
+
+// stackExchangeResponse represents the Stack Exchange API v2.3 search/excerpts response.
+type stackExchangeResponse struct {
+	Items []stackExchangeItem `json:"items"`
+}
+
+type stackExchangeItem struct {
+	Body      string `json:"body"`
+	Excerpt   string `json:"excerpt"`
+	QuestionID int   `json:"question_id"`
+}
+
+func (s *StackOverflowSource) Sweep(ctx context.Context, _ string, out chan<- recon.Finding) error {
+	base := s.BaseURL
+	if base == "" {
+		base = "https://api.stackexchange.com"
+	}
+	client := s.Client
+	if client == nil {
+		client = NewClient()
+	}
+
+	queries := BuildQueries(s.Registry, "stackoverflow")
+	if len(queries) == 0 {
+		return nil
+	}
+
+	for _, q := range queries {
+		if err := ctx.Err(); err != nil {
+			return err
+		}
+
+		if s.Limiters != nil {
+			if err := s.Limiters.Wait(ctx, s.Name(), s.RateLimit(), s.Burst(), false); err != nil {
+				return err
+			}
+		}
+
+		searchURL := fmt.Sprintf("%s/2.3/search/excerpts?order=desc&sort=relevance&q=%s&site=stackoverflow",
+			base, url.QueryEscape(q))
+		req, err := http.NewRequestWithContext(ctx, http.MethodGet, searchURL, nil)
+		if err != nil {
+			continue
+		}
+		req.Header.Set("Accept", "application/json")
+
+		resp, err := client.Do(ctx, req)
+		if err != nil {
+			continue
+		}
+
+		body, err := io.ReadAll(io.LimitReader(resp.Body, 256*1024))
+		_ = resp.Body.Close()
+		if err != nil {
+			continue
+		}
+
+		var result stackExchangeResponse
+		if err := json.Unmarshal(body, &result); err != nil {
+			continue
+		}
+
+		for _, item := range result.Items {
+			content := item.Body + " " + item.Excerpt
+			if ciLogKeyPattern.MatchString(content) {
+				itemURL := fmt.Sprintf("https://stackoverflow.com/q/%d", item.QuestionID)
+				out <- recon.Finding{
+					ProviderName: q,
+					Source:       itemURL,
+					SourceType:   "recon:stackoverflow",
+					Confidence:   "medium",
+					DetectedAt:   time.Now(),
+				}
+			}
+		}
+	}
+	return nil
+}