jwt.go
func PeekHeaderField(buf []byte, field string) (string, error) {
	return peekField(buf, field, tokenPositionHeader)
}
func PeekHeaderField(buf []byte, field string) (string, error) {
	return peekField(buf, field, tokenPositionHeader)
}
func PeekHeaderField ( buf [ ] byte , field string ) ( string , error ) { return peekField ( buf , field , tokenPositionHeader ) }
// PeekHeaderField extracts the specified field from the serialized JWT buf's
// header. An error will be returned if the field is not present in the decoded
// header.
PeekHeaderField extracts the specified field from the serialized JWT buf s header . An error will be returned if the field is not present in the decoded header .