add functions to remove confidential information (#6516)

This commit adds two functions for removing
confidential information - like SSE-C keys -
from HTTP headers / object metadata.

This creates a central point grouping all
headers/entries which must be filtered / removed.

See also https://github.com/minio/minio/pull/6489#discussion_r219797993
of #6489

cmd/crypto/header_test.go

@@ -16,6 +16,7 @@ package crypto
 
 import (
 	"net/http"
+	"sort"
 	"testing"
 )
 
@@ -337,3 +338,102 @@ func TestSSECopyParse(t *testing.T) {
 		}
 	}
 }
+
+var removeSensitiveHeadersTests = []struct {
+	Header, ExpectedHeader http.Header
+}{
+	{
+		Header: http.Header{
+			SSECKey:    []string{""},
+			SSECopyKey: []string{""},
+		},
+		ExpectedHeader: http.Header{},
+	},
+	{ // Standard SSE-C request headers
+		Header: http.Header{
+			SSECAlgorithm: []string{SSEAlgorithmAES256},
+			SSECKey:       []string{"MzJieXRlc2xvbmdzZWNyZXRrZXltdXN0cHJvdmlkZWQ="},
+			SSECKeyMD5:    []string{"7PpPLAK26ONlVUGOWlusfg=="},
+		},
+		ExpectedHeader: http.Header{
+			SSECAlgorithm: []string{SSEAlgorithmAES256},
+			SSECKeyMD5:    []string{"7PpPLAK26ONlVUGOWlusfg=="},
+		},
+	},
+	{ // Standard SSE-C + SSE-C-copy request headers
+		Header: http.Header{
+			SSECAlgorithm: []string{SSEAlgorithmAES256},
+			SSECKey:       []string{"MzJieXRlc2xvbmdzZWNyZXRrZXltdXN0cHJvdmlkZWQ="},
+			SSECKeyMD5:    []string{"7PpPLAK26ONlVUGOWlusfg=="},
+			SSECopyKey:    []string{"MzJieXRlc2xvbmdzZWNyZXRrZXltdXN0cHJvdmlkZWQ="},
+			SSECopyKeyMD5: []string{"7PpPLAK26ONlVUGOWlusfg=="},
+		},
+		ExpectedHeader: http.Header{
+			SSECAlgorithm: []string{SSEAlgorithmAES256},
+			SSECKeyMD5:    []string{"7PpPLAK26ONlVUGOWlusfg=="},
+			SSECopyKeyMD5: []string{"7PpPLAK26ONlVUGOWlusfg=="},
+		},
+	},
+	{ // Standard SSE-C + metadata request headers
+		Header: http.Header{
+			SSECAlgorithm:       []string{SSEAlgorithmAES256},
+			SSECKey:             []string{"MzJieXRlc2xvbmdzZWNyZXRrZXltdXN0cHJvdmlkZWQ="},
+			SSECKeyMD5:          []string{"7PpPLAK26ONlVUGOWlusfg=="},
+			"X-Amz-Meta-Test-1": []string{"Test-1"},
+		},
+		ExpectedHeader: http.Header{
+			SSECAlgorithm:       []string{SSEAlgorithmAES256},
+			SSECKeyMD5:          []string{"7PpPLAK26ONlVUGOWlusfg=="},
+			"X-Amz-Meta-Test-1": []string{"Test-1"},
+		},
+	},
+}
+
+func TestRemoveSensitiveHeaders(t *testing.T) {
+	isEqual := func(x, y http.Header) bool {
+		if len(x) != len(y) {
+			return false
+		}
+		for k, v := range x {
+			u, ok := y[k]
+			if !ok || len(v) != len(u) {
+				return false
+			}
+			sort.Strings(v)
+			sort.Strings(u)
+			for j := range v {
+				if v[j] != u[j] {
+					return false
+				}
+			}
+		}
+		return true
+	}
+	areKeysEqual := func(h http.Header, metadata map[string]string) bool {
+		if len(h) != len(metadata) {
+			return false
+		}
+		for k := range h {
+			if _, ok := metadata[k]; !ok {
+				return false
+			}
+		}
+		return true
+	}
+
+	for i, test := range removeSensitiveHeadersTests {
+		metadata := make(map[string]string, len(test.Header))
+		for k := range test.Header {
+			metadata[k] = "" // set metadata key - we don't care about the value
+		}
+
+		RemoveSensitiveHeaders(test.Header)
+		if !isEqual(test.ExpectedHeader, test.Header) {
+			t.Errorf("Test %d: filtered headers do not match expected headers - got: %v , want: %v", i, test.Header, test.ExpectedHeader)
+		}
+		RemoveSensitiveEntries(metadata)
+		if !areKeysEqual(test.ExpectedHeader, metadata) {
+			t.Errorf("Test %d: filtered headers do not match expected headers - got: %v , want: %v", i, test.Header, test.ExpectedHeader)
+		}
+	}
+}