Parse external request id from request headers, and print it in access log (#22906)

Close: #22890.

---
### Configure in .ini file:
```ini
[log]
REQUEST_ID_HEADERS = X-Request-ID, X-Trace-Id
```

### Params in Request Header
```
X-Trace-ID: trace-id-1q2w3e4r
```

![image](https://user-images.githubusercontent.com/33891828/218665296-8fd19a0f-ada6-4236-8bdb-f99201c703e8.png)



### Log output:

![image](https://user-images.githubusercontent.com/33891828/218665225-cc242a57-4ffc-449a-a1f6-f45ded0ead60.png)

2 files changed, 36 insertions, 0 deletions

diff --git a/modules/context/access_log.go b/modules/context/access_log.go
index 1aaba9dc2d..515682b64b 100644
--- a/modules/context/access_log.go
+++ b/modules/context/access_log.go
@@ -6,7 +6,9 @@ package context
 import (
 	"bytes"
 	"context"
+	"fmt"
 	"net/http"
+	"strings"
 	"text/template"
 	"time"
 
@@ -20,13 +22,39 @@ type routerLoggerOptions struct {
 	Start          *time.Time
 	ResponseWriter http.ResponseWriter
 	Ctx            map[string]interface{}
+	RequestID      *string
 }
 
 var signedUserNameStringPointerKey interface{} = "signedUserNameStringPointerKey"
 
+const keyOfRequestIDInTemplate = ".RequestID"
+
+// According to:
+// TraceId: A valid trace identifier is a 16-byte array with at least one non-zero byte
+// MD5 output is 16 or 32 bytes: md5-bytes is 16, md5-hex is 32
+// SHA1: similar, SHA1-bytes is 20, SHA1-hex is 40.
+// UUID is 128-bit, 32 hex chars, 36 ASCII chars with 4 dashes
+// So, we accept a Request ID with a maximum character length of 40
+const maxRequestIDByteLength = 40
+
+func parseRequestIDFromRequestHeader(req *http.Request) string {
+	requestID := "-"
+	for _, key := range setting.Log.RequestIDHeaders {
+		if req.Header.Get(key) != "" {
+			requestID = req.Header.Get(key)
+			break
+		}
+	}
+	if len(requestID) > maxRequestIDByteLength {
+		requestID = fmt.Sprintf("%s...", requestID[:maxRequestIDByteLength])
+	}
+	return requestID
+}
+
 // AccessLogger returns a middleware to log access logger
 func AccessLogger() func(http.Handler) http.Handler {
 	logger := log.GetLogger("access")
+	needRequestID := len(setting.Log.RequestIDHeaders) > 0 && strings.Contains(setting.Log.AccessLogTemplate, keyOfRequestIDInTemplate)
 	logTemplate, _ := template.New("log").Parse(setting.Log.AccessLogTemplate)
 	return func(next http.Handler) http.Handler {
 		return http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
@@ -34,6 +62,11 @@ func AccessLogger() func(http.Handler) http.Handler {
 			identity := "-"
 			r := req.WithContext(context.WithValue(req.Context(), signedUserNameStringPointerKey, &identity))
 
+			var requestID string
+			if needRequestID {
+				requestID = parseRequestIDFromRequestHeader(req)
+			}
+
 			next.ServeHTTP(w, r)
 			rw := w.(ResponseWriter)
 
@@ -47,6 +80,7 @@ func AccessLogger() func(http.Handler) http.Handler {
 					"RemoteAddr": req.RemoteAddr,
 					"Req":        req,
 				},
+				RequestID: &requestID,
 			})
 			if err != nil {
 				log.Error("Could not set up chi access logger: %v", err.Error())
diff --git a/modules/setting/log.go b/modules/setting/log.go
index 5448650aad..dabdb543ab 100644
--- a/modules/setting/log.go
+++ b/modules/setting/log.go
@@ -38,6 +38,7 @@ var Log struct {
 	EnableAccessLog   bool
 	AccessLogTemplate string
 	BufferLength      int64
+	RequestIDHeaders  []string
 }
 
 // GetLogDescriptions returns a race safe set of descriptions
@@ -153,6 +154,7 @@ func loadLogFrom(rootCfg ConfigProvider) {
 	Log.AccessLogTemplate = sec.Key("ACCESS_LOG_TEMPLATE").MustString(
 		`{{.Ctx.RemoteAddr}} - {{.Identity}} {{.Start.Format "[02/Jan/2006:15:04:05 -0700]" }} "{{.Ctx.Req.Method}} {{.Ctx.Req.URL.RequestURI}} {{.Ctx.Req.Proto}}" {{.ResponseWriter.Status}} {{.ResponseWriter.Size}} "{{.Ctx.Req.Referer}}\" \"{{.Ctx.Req.UserAgent}}"`,
 	)
+	Log.RequestIDHeaders = sec.Key("REQUEST_ID_HEADERS").Strings(",")
 	// the `MustString` updates the default value, and `log.ACCESS` is used by `generateNamedLogger("access")` later
 	_ = rootCfg.Section("log").Key("ACCESS").MustString("file")