Fix auth's wildcard Match function

[nopcoder]

Address performance and malicious usage.
Fix #1996

Added unit test code from MinIO for testing the functionality.

Used the following modified benchmark code supplied by @arielshaqed to test code for malicious usage:

package wildcard

import (
	"strings"
	"testing"
)

func BenchmarkMatch(b *testing.B) {
	const pattern = "a*b*c*z"
	str := strings.Repeat("a", 1000) + strings.Repeat("b", 1000) + strings.Repeat("c", 1000)
	for i := 0; i < b.N; i++ {
		if Match(pattern, str) {
			b.Errorf("Expecteded '%s' NOT to match '%s'", str, pattern)
		}
	}
}

func BenchmarkMatchDuh(b *testing.B) {
	const pattern = "a*a*a*z"
	str := strings.Repeat("a", 2000)
	for i := 0; i < b.N; i++ {
		if Match(pattern, str) {
			b.Errorf("Expecteded '%s' NOT to match '%s'", str, pattern)
		}
	}
}

Test results of current implementation:

BenchmarkMatch-10                      1        4474831292 ns/op
BenchmarkMatchDuh-10                   1        11981327834 ns/op

Test results of the new implementation:

BenchmarkMatch-10                 176950              6804 ns/op
BenchmarkMatchDuh-10              264994              4511 ns/op

[arielshaqed]

Nice one, thanks!

I had some difficulty understanding the algorithm at first (it doesn't backtrack or consider more than one possibility at any point!). For future readers and especially future me here are my notes on how it works. So very safe to skip this!

Call a "fixword" a maximal portion of the pattern consisting only of regular characters and ?s. So a fixword has to begin after * or at the beginning of the string, and it has to end before * or at the end of the string.

Each fixword matches a fixed length of string. Now a pattern is a list of fixwords separated by *s. Consider a fixword that is not preceded by a *; that's an easy match to find because it can only be at one place. Consider a fixword that is preceded by a *; if it matches at multiple places then it is always safe to match it at the first possible location: either the pattern ends after that fixword in which case there's only one possible location, or the pattern continues with *, in which case that * can "expand" to pick up all characters and the next match of the fixword.

Either way, it's safe, so everything works.

[nopcoder]

@arielshaqed thank you, credit to the Go team - I'll add the above explanation to the code so other will enjoy it.