TUN-6772: Add a JWT Validator as an ingress verifier

This adds a new verifier interface that can be attached to ingress.Rule.
This would act as a middleware layer that gets executed at the start of
proxy.ProxyHTTP.

A jwt validator implementation for this verifier is also provided. The
validator downloads the public key from the access teams endpoint and
uses it to verify the JWT sent to cloudflared with the audtag (clientID)
information provided in the config.

vendor/golang.org/x/xerrors/doc.go

@@ -5,7 +5,8 @@
 // Package xerrors implements functions to manipulate errors.
 //
 // This package is based on the Go 2 proposal for error values:
-//   https://golang.org/design/29934-error-values
+//
+//	https://golang.org/design/29934-error-values
 //
 // These functions were incorporated into the standard library's errors package
 // in Go 1.13:

vendor/golang.org/x/xerrors/fmt.go

@@ -33,6 +33,9 @@ const percentBangString = "%!"
 // It is invalid to include more than one %w verb or to supply it with an
 // operand that does not implement the error interface. The %w verb is otherwise
 // a synonym for %v.
+//
+// Note that as of Go 1.13, the fmt.Errorf function will do error formatting,
+// but it will not capture a stack backtrace.
 func Errorf(format string, a ...interface{}) error {
 	format = formatPlusW(format)
 	// Support a ": %[wsv]" suffix, which works well with xerrors.Formatter.

vendor/golang.org/x/xerrors/wrap.go

@@ -35,6 +35,8 @@ func (e noWrapper) FormatError(p Printer) (next error) {
 
 // Unwrap returns the result of calling the Unwrap method on err, if err implements
 // Unwrap. Otherwise, Unwrap returns nil.
+//
+// Deprecated: As of Go 1.13, use errors.Unwrap instead.
 func Unwrap(err error) error {
 	u, ok := err.(Wrapper)
 	if !ok {
@@ -47,6 +49,8 @@ func Unwrap(err error) error {
 //
 // An error is considered to match a target if it is equal to that target or if
 // it implements a method Is(error) bool such that Is(target) returns true.
+//
+// Deprecated: As of Go 1.13, use errors.Is instead.
 func Is(err, target error) bool {
 	if target == nil {
 		return err == target
@@ -77,6 +81,8 @@ func Is(err, target error) bool {
 //
 // The As method should set the target to its value and return true if err
 // matches the type to which target points.
+//
+// Deprecated: As of Go 1.13, use errors.As instead.
 func As(err error, target interface{}) bool {
 	if target == nil {
 		panic("errors: target cannot be nil")