iam: optionally require an iam: grant for self-service access-key actions (#11937)

* iam: optionally require an iam: grant for self-service access-key actions

AuthorizeIamAction lets every authenticated identity run CreateAccessKey,
DeleteAccessKey, UpdateAccessKey, ListAccessKeys and GetUser on itself with
no grant. On AWS these actions need an IAM policy (the usual one grants them
on arn:aws:iam::*:user/${aws:username}); nothing is allowed implicitly.

Where identities hold data-plane rights only, the implicit carve-out lets a
leaked key mint further keys for its own identity, with no cap, that keep
working after the operator deletes the key that leaked; it can also
deactivate or delete the keys the operator issued.

A new option, off by default, makes these actions need the iam:<Action> grant
like every other IAM action: -s3.iam.selfServiceRequiresGrant on weed
server, filer and mini, -iam.selfServiceRequiresGrant on weed s3. With it
set, the grant is authorized against the target user's ARN, the caller's own
when UserName is empty, so a policy can confine it to the caller's own keys
(Resource arn:aws:iam:::user/${aws:username}), the same resource scoping
CreateServiceAccount already uses. The admin and iam:* grants are unchanged;
with the option off nothing changes.

Tests (s3api_embedded_iam_authz_test.go): with the option set, an identity
holding only s3:* and a bare identity are refused all five actions on an
empty, own and other target (fails without the change); a grant on the
caller's own user ARN, literal or ${aws:username}, allows them on itself and
not on another user; the admin and an iam:* grant keep every action; with the
option off self-service is allowed as before.

* iam: wire selfServiceRequiresGrant on the standalone iam server

Every other command that runs the embedded IAM API accepts the flag; the
deprecated weed iam could not enable the enforcement at all.

* iam: wire selfServiceRequiresGrant on weed server and filer -iam

The IamOptions used by 'weed server -iam' and 'weed filer -iam' never
received the flag, so startIamServer dereferenced a nil pointer at
startup. Share the -s3.iam.selfServiceRequiresGrant pointer with them.

---------

Co-authored-by: Javier de la Torre <jatorre@lakehousebox.com>
Co-authored-by: Chris Lu <chrislusf@users.noreply.github.com>

weed/command/server.go

@@ -200,6 +200,7 @@ func init() {
 	s3Options.cacheSizeMB = cmdServer.Flag.Int64("s3.cacheCapacityMB", 0, "in-memory chunk cache capacity in MB for S3 GETs shared across requests (0 disables)")
 	s3Options.readerCacheSizeMB = cmdServer.Flag.Int64("s3.readerCacheSizeMB", 0, "memory budget in MiB for downloaded and in-flight reader buffers across all S3 GETs (0 means unlimited)")
 	s3Options.allowUntrustedRemoteEndpoints = cmdServer.Flag.Bool("s3.allowUntrustedRemoteEndpoints", false, allowUntrustedRemoteEndpointsUsage)
+	s3Options.iamSelfServiceRequiresGrant = cmdServer.Flag.Bool("s3.iam.selfServiceRequiresGrant", false, iamSelfServiceRequiresGrantUsage)
 
 	sftpOptions.port = cmdServer.Flag.Int("sftp.port", 2022, "SFTP server listen port")
 	sftpOptions.sshPrivateKey = cmdServer.Flag.String("sftp.sshPrivateKey", "", "path to the SSH private key file for host authentication")
@@ -215,6 +216,7 @@ func init() {
 	sftpOptions.dataCenter = cmdServer.Flag.String("sftp.dataCenter", "", "prefer to read and write to volumes in this data center")
 	sftpOptions.localSocket = cmdServer.Flag.String("sftp.localSocket", "", "default to /tmp/seaweedfs-sftp-<port>.sock")
 	iamOptions.port = cmdServer.Flag.Int("iam.port", 8111, "iam server http listen port")
+	iamOptions.selfServiceRequiresGrant = s3Options.iamSelfServiceRequiresGrant
 
 	webdavOptions.port = cmdServer.Flag.Int("webdav.port", 7333, "webdav server http listen port")
 	webdavOptions.collection = cmdServer.Flag.String("webdav.collection", "", "collection to create the files")