rebase: Bump github.com/hashicorp/vault from 1.4.2 to 1.9.9

Bumps [github.com/hashicorp/vault](https://github.com/hashicorp/vault) from 1.4.2 to 1.9.9.
- [Release notes](https://github.com/hashicorp/vault/releases)
- [Changelog](https://github.com/hashicorp/vault/blob/main/CHANGELOG.md)
- [Commits](https://github.com/hashicorp/vault/compare/v1.4.2...v1.9.9)

---
updated-dependencies:
- dependency-name: github.com/hashicorp/vault
  dependency-type: indirect
...

Signed-off-by: dependabot[bot] <support@github.com>

vendor/github.com/grpc-ecosystem/grpc-gateway/v2/runtime/context.go

@@ -41,6 +41,12 @@ var (
 	DefaultContextTimeout = 0 * time.Second
 )
 
+// malformedHTTPHeaders lists the headers that the gRPC server may reject outright as malformed.
+// See https://github.com/grpc/grpc-go/pull/4803#issuecomment-986093310 for more context.
+var malformedHTTPHeaders = map[string]struct{}{
+	"connection": {},
+}
+
 type (
 	rpcMethodKey       struct{}
 	httpPathPatternKey struct{}
@@ -172,11 +178,17 @@ type serverMetadataKey struct{}
 
 // NewServerMetadataContext creates a new context with ServerMetadata
 func NewServerMetadataContext(ctx context.Context, md ServerMetadata) context.Context {
+	if ctx == nil {
+		ctx = context.Background()
+	}
 	return context.WithValue(ctx, serverMetadataKey{}, md)
 }
 
 // ServerMetadataFromContext returns the ServerMetadata in ctx
 func ServerMetadataFromContext(ctx context.Context) (md ServerMetadata, ok bool) {
+	if ctx == nil {
+		return md, false
+	}
 	md, ok = ctx.Value(serverMetadataKey{}).(ServerMetadata)
 	return
 }
@@ -308,6 +320,13 @@ func isPermanentHTTPHeader(hdr string) bool {
 	return false
 }
 
+// isMalformedHTTPHeader checks whether header belongs to the list of
+// "malformed headers" and would be rejected by the gRPC server.
+func isMalformedHTTPHeader(header string) bool {
+	_, isMalformed := malformedHTTPHeaders[strings.ToLower(header)]
+	return isMalformed
+}
+
 // RPCMethod returns the method string for the server context. The returned
 // string is in the format of "/package.service/method".
 func RPCMethod(ctx context.Context) (string, bool) {