Add parsing logic for User-Agent headers (#5645)

* feat(ts_telemetry): add parsing logic for user agent headers

* feat(ts_telemetry): update gRPC observability for user-agent headers

* feat(ts_telemetry): add observation tags

* feat(ts_telemetry): Resolved comments

* feat(ts_telemetry): Removed loop variable capture

* feat(ts_telemetry): Updated userAgentKey to be inline

* feat(ts_telemetry): Add support for userAgent as per RFC 9110

* feat(ts_telemetry): Resolved comments

* Fix newline

* feat(ts_telemetry): Moved user-agent parsing to interceptor

* feat(ts_telemetry): Added user-agent parsing complex test case

* Update userAgentsKey comment

Co-authored-by: Johan Brandhorst-Satzkorn <johan.brandhorst@gmail.com>

* feat(ts_telemetry): Updated changelog

* feat(ts_telemetry): Resolved comments

---------

Co-authored-by: Johan Brandhorst-Satzkorn <johan.brandhorst@gmail.com>

internal/daemon/controller/interceptor.go

@@ -9,7 +9,9 @@ import (
 	"fmt"
 	"net/http"
 	"reflect"
+	"regexp"
 	"runtime/debug"
+	"strings"
 	"time"
 
 	grpc_recovery "github.com/grpc-ecosystem/go-grpc-middleware/recovery"
@@ -27,6 +29,7 @@ import (
 	"github.com/hashicorp/boundary/internal/kms"
 	"github.com/hashicorp/boundary/internal/requests"
 	"github.com/hashicorp/go-uuid"
+	"github.com/hashicorp/go-version"
 	"github.com/mr-tron/base58"
 	"google.golang.org/grpc"
 	"google.golang.org/grpc/codes"
@@ -45,8 +48,16 @@ const (
 	// apiErrHeader defines an http header for encoded api errors from the
 	// grpc server.
 	apiErrHeader = "x-api-err"
+
+	// boundaryClientAgentProduct defines the product name used to identify the
+	// Boundary client agent in user-agent parsing and validation logic.
+	boundaryClientAgentProduct = "Boundary-client-agent"
 )
 
+// Regular expression to parse user-agent product, version, and comments
+// Follows the structure defined in RFC 9110: https://datatracker.ietf.org/doc/html/rfc9110#name-user-agent
+var userAgentRegex = regexp.MustCompile(`(?P<product>[^\s/()]+)/(?P<version>[^\s()]+)(?: \((?P<comments>[^)]+)\))?`)
+
 // customContextServerStream wraps the grpc.ServerStream interface and lets us
 // set a custom context
 type customContextServerStream struct {
@@ -448,14 +459,24 @@ func eventsRequestInterceptor(
 		_ *grpc.UnaryServerInfo,
 		handler grpc.UnaryHandler) (any, error,
 	) {
+		var userAgents []*event.UserAgent
+		if md, ok := metadata.FromIncomingContext(interceptorCtx); ok {
+			if values := md.Get(userAgentsKey); len(values) > 0 {
+				userAgents = parseUserAgents(values[0])
+			}
+		}
 		if msg, ok := req.(proto.Message); ok {
 			// Clone the request before writing it to the audit log,
 			// in case downstream interceptors modify it.
 			clonedMsg := proto.Clone(msg)
+			request := &event.Request{
+				Details:    clonedMsg,
+				UserAgents: userAgents,
+			}
 			if err := event.WriteAudit(interceptorCtx, op, event.WithRequest(&event.Request{Details: clonedMsg})); err != nil {
 				return req, status.Errorf(codes.Internal, "unable to write request msg audit: %s", err)
 			}
-			if err := event.WriteObservation(interceptorCtx, op, event.WithRequest(&event.Request{Details: clonedMsg})); err != nil {
+			if err := event.WriteObservation(interceptorCtx, op, event.WithRequest(request)); err != nil {
 				return req, status.Errorf(codes.Internal, "unable to write request msg observation: %s", err)
 			}
 		}
@@ -464,6 +485,53 @@ func eventsRequestInterceptor(
 	}
 }
 
+// parseUserAgents extracts structured UserAgent data from a raw User-Agent header string.
+// Version validation is applied only to Boundary-client-agent entries, which are excluded
+// if the version starts with 'v' or is not a valid semantic version.
+// Comments are split and normalized into a slice of strings.
+func parseUserAgents(rawUserAgent string) []*event.UserAgent {
+	var userAgents []*event.UserAgent
+	matches := userAgentRegex.FindAllStringSubmatch(rawUserAgent, -1)
+
+	for _, match := range matches {
+		product := strings.TrimSpace(match[1])
+		agentVersion := strings.TrimSpace(match[2])
+
+		// Only apply version validation for Boundary-client-agent
+		if product == boundaryClientAgentProduct {
+			if strings.HasPrefix(agentVersion, "v") {
+				// Invalid version format (starting with 'v')
+				continue
+			}
+			if _, err := version.NewSemver(agentVersion); err != nil {
+				// Invalid version
+				continue
+			}
+		}
+
+		agentData := &event.UserAgent{
+			Product:        product,
+			ProductVersion: agentVersion,
+		}
+
+		if len(match) > 3 && match[3] != "" {
+			// Clean up and split comments
+			commentsRaw := strings.Split(match[3], ";")
+			var comments []string
+			for _, c := range commentsRaw {
+				if trimmed := strings.TrimSpace(c); trimmed != "" {
+					comments = append(comments, trimmed)
+				}
+			}
+			if len(comments) > 0 {
+				agentData.Comments = comments
+			}
+		}
+		userAgents = append(userAgents, agentData)
+	}
+	return userAgents
+}
+
 func eventsResponseInterceptor(
 	_ context.Context,
 ) grpc.UnaryServerInterceptor {