Fix credential parsing in signature v4 (#7377)

Fixes #7376

cmd/signature-v4-parser.go

@@ -66,7 +66,7 @@ func getReqAccessKeyV4(r *http.Request, region string, stype serviceType) (auth.
 
 // parse credentialHeader string into its structured form.
 func parseCredentialHeader(credElement string, region string, stype serviceType) (ch credentialHeader, aec APIErrorCode) {
-	creds := strings.Split(strings.TrimSpace(credElement), "=")
+	creds := strings.SplitN(strings.TrimSpace(credElement), "=", 2)
 	if len(creds) != 2 {
 		return ch, ErrMissingFields
 	}

cmd/signature-v4-parser_test.go

@@ -216,6 +216,25 @@ func TestParseCredentialHeader(t *testing.T) {
 				"aws4_request"),
 			expectedErrCode: ErrNone,
 		},
+		// Test Case - 11.
+		// Test case with right inputs -> AccessKey contains `=`. See minio/#7376
+		// "aws4_request" is the valid request version.
+		{
+			inputCredentialStr: generateCredentialStr(
+				"LOCALKEY/DEV/1=",
+				sampleTimeStr,
+				"us-west-1",
+				"s3",
+				"aws4_request"),
+			expectedCredentials: generateCredentials(
+				t,
+				"LOCALKEY/DEV/1=",
+				sampleTimeStr,
+				"us-west-1",
+				"s3",
+				"aws4_request"),
+			expectedErrCode: ErrNone,
+		},
 	}
 
 	for i, testCase := range testCases {