Add role ARN support for OIDC identity provider (#13651)

- Allows setting a role policy parameter when configuring OIDC provider

- When role policy is set, the server prints a role ARN usable in STS API requests

- The given role policy is applied to STS API requests when the roleARN parameter is provided.

- Service accounts for role policy are also possible and work as expected.

internal/arn/arn.go

@@ -0,0 +1,147 @@
+// Copyright (c) 2015-2021 MinIO, Inc.
+//
+// This file is part of MinIO Object Storage stack
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package arn
+
+import (
+	"fmt"
+	"regexp"
+	"strings"
+)
+
+// ARN structure:
+//
+// arn:partition:service:region:account-id:resource-type/resource-id
+//
+// In this implementation, account-id is empty.
+//
+// Reference: https://docs.aws.amazon.com/general/latest/gr/aws-arns-and-namespaces.html
+
+type arnPartition string
+
+const (
+	arnPartitionMinio arnPartition = "minio"
+)
+
+type arnService string
+
+const (
+	arnServiceIAM arnService = "iam"
+)
+
+type arnResourceType string
+
+const (
+	arnResourceTypeRole arnResourceType = "role"
+)
+
+// ARN - representation of resources based on AWS ARNs.
+type ARN struct {
+	Partition    arnPartition
+	Service      arnService
+	Region       string
+	ResourceType arnResourceType
+	ResourceID   string
+}
+
+var (
+	// Allows lower-case chars, numbers, '.', '-', '_' and '/'. Starts with
+	// a letter or digit. At least 1 character long.
+	validResourceIDRegex = regexp.MustCompile(`^[a-z0-9][a-z0-9_/\.-]*$`)
+)
+
+// NewIAMRoleARN - returns an ARN for a role in MinIO.
+func NewIAMRoleARN(resourceID, serverRegion string) (ARN, error) {
+	if !validResourceIDRegex.MatchString(resourceID) {
+		return ARN{}, fmt.Errorf("Invalid resource ID: %s", resourceID)
+	}
+	return ARN{
+		Partition:    arnPartitionMinio,
+		Service:      arnServiceIAM,
+		Region:       serverRegion,
+		ResourceType: arnResourceTypeRole,
+		ResourceID:   resourceID,
+	}, nil
+}
+
+// String - returns string representation of the ARN.
+func (arn ARN) String() string {
+	return strings.Join(
+		[]string{
+			"arn",
+			string(arn.Partition),
+			string(arn.Service),
+			arn.Region,
+			"", // account-id is always empty in this implementation
+			string(arn.ResourceType) + "/" + arn.ResourceID,
+		},
+		":",
+	)
+}
+
+// Parse - parses an ARN string into a type.
+func Parse(arnStr string) (arn ARN, err error) {
+	ps := strings.Split(arnStr, ":")
+	if len(ps) != 6 ||
+		ps[0] != "arn" {
+		err = fmt.Errorf("Invalid ARN string format")
+		return
+	}
+
+	if ps[1] != string(arnPartitionMinio) {
+		err = fmt.Errorf("Invalid ARN - bad partition field")
+		return
+	}
+
+	if ps[2] != string(arnServiceIAM) {
+		err = fmt.Errorf("Invalid ARN - bad service field")
+		return
+	}
+
+	// ps[3] is region and is not validated here. If the region is invalid,
+	// the ARN would not match any configured ARNs in the server.
+
+	if ps[4] != "" {
+		err = fmt.Errorf("Invalid ARN - unsupported account-id field")
+		return
+	}
+
+	res := strings.SplitN(ps[5], "/", 2)
+	if len(res) != 2 {
+		err = fmt.Errorf("Invalid ARN - resource does not contain a \"/\"")
+		return
+	}
+
+	if res[0] != string(arnResourceTypeRole) {
+		err = fmt.Errorf("Invalid ARN: resource type is invalid.")
+		return
+	}
+
+	if !validResourceIDRegex.MatchString(res[1]) {
+		err = fmt.Errorf("Invalid resource ID: %s", res[1])
+		return
+	}
+
+	arn = ARN{
+		Partition:    arnPartitionMinio,
+		Service:      arnServiceIAM,
+		Region:       ps[3],
+		ResourceType: arnResourceTypeRole,
+		ResourceID:   res[1],
+	}
+	return
+}