TLS (“SSL”) Quirks in OpenSim

This is not a post about my ongoing struggles to make OpenSim work with TLS and communicate properly with other grids, using a transparent Nginx reverse proxy. I suspect there may be one or two bugs to report but I am still investigating numerous issues, particularly around why the XMLRPC method verify_agent seems to fail to reach the target grid consistently – is it my proxy settings or is it something in OpenSim?

I am going to write about the alleged “out of band” TLS settings, a topic which confused me for some time. You will find these in Robust[.HG].ini (for my earlier work on TLS for the simulator, please see my earlier post, which makes edits to OpenSim.ini). In fact, despite my earlier credence in this statement, it is potentially misleading. It is in fact possible to add a native HTTPS port to the simulator, to set it as the main listener port rather than as the additional port, and to set it up with TLS provided externally. There are some considerable quirks in this system – and one major drawback that means that you will continue to need to use an external reverse proxy like Nginx to operate a grid using TLS.

I will be studiously avoiding the common and erroneous use of the term SSL for TLS, since the use of SSL instead of its successor TLS for HTTPS and similar protocols has long been compromised and is both insecure and deprecated. In fact it is wisest only to use TLS versions 1.2 and 1.3 if at all possible, never version 1.0. It may still be necessary to use version 1.1 for some limited purposes but I shall not address that further here. Both 1.0 and 1.1 have been deprecated by major browsers since March 2020.

The settings in question under [Network] are https_listener, https_main and https_external (of which the latter remains undocumented, even in OpenSimDefaults.ini).

The first of these, https_listener = True, adds an additional secure HTTPS (TLS) port as documented. You will also need to set https_port = 9002 (or whatever suits your setup, but I am popularising 9002 and 9003 for the defaults for TLS), cert_path = “path/to/cert.p12” (location of the X509 certificate) and cert_pass = “yourpassword”, as well as possibly needing to look again under [Startup] at NoVerifyCertChain = true and NoVerifyCertHostname = true (set to false if you are using a certificate authority to validate your certificates via LetsEncrypt or some other authority).

The next setting https_main = True sets the main listener as the HTTPS port. However, whether by design or by oversight, it does not transfer any of the HTTP handlers (use show http-handlers on the Robust console to show these) to the HTTPS listener port. This is a problem for Hypergrid (and presumably for the purposes of all the other handlers too!) since you will be unable to verify the identity of the agent and the client without the relevant XMLRPC methods. For this reason, setting up a grid to use TLS still requires the use of Nginx as a reverse proxy. (I am still having problems getting this to work despite successful manual XMLRPC calls to the ports with cURL to check that the correct results are in fact returned from the server.) This quirk is really quite annoying but I do not know if there is some reason for it. Since this is the main public port, I can see no reason not to switch it over or duplicate these endpoints. Another less important quirk is that port is not replaced, irrespective of how you set https_main, and that https_port is additional, similar to the situation on the simulator that I documented in my earlier post. This is no problem: you don’t have to let it through your firewall.

Ed. [2022-02-18 10:58]: Are the missing HTTP handlers related to this commit?

The third quirk relates to the entirely undocumented https_external setting. I discovered this by looking at the code in Framework/NetworkServersInfo.cs (and, for example, in the OpenSim Mantis such as in this feature request). This is a very peculiar setting indeed because, if https_external = True and https_listener = True together, the https_port port will be added without TLS i.e. it will be reachable only by the protocol http:// and not by https:// on the server. It will then require an external proxy like Nginx to provide the latter (for which see my comments above on the ongoing issues that I am testing). In essence, despite the name https_port, it is then an additional HTTP port without any of the HTTP handlers that are provided on port. You then have two plain HTTP ports. That seems rather eccentric, but it works and is logical, though it is counter-intuitive. You wouldn’t guess this without some help, especially as it isn’t documented.

To summarise, the description of these settings as only being useful for “out of band” purposes like the remote console is still accurate because the HTTP handlers are not available, whether it is the secondary or the main public port on the Robust server. If these were transferred and/or duplicated then it follows that it would also be of primary use in setting up TLS on Robust without the need for a reverse proxy. I would like to see this happen: it might help with my struggles with the Hypergrid with TLS.

I hope this post is of use to OpenSim developers, testers and grid admins alike. I will document what I suspect may be problems/bugs in using TLS with reverse proxies in another post when I can (still testing).

Lastly, I repeat my assertion that this is a priority matter and that all grids should at least use TLS for the login server so that passwords are not broadcast in the clear – Ed. note that the SceneGate viewer actually warns you about this by default unless you tell it not to after the first time. That is the industry standard for a reason. I accept the arguments about the excessive overheads of encryption for other purposes, although I am reminded of SL being hacked by giant penises back in the day and thus suggest that it might be an idea to secure some other public data transmissions too. The overheads are not that much in practice on modern hardware and with modern compression standards, and you don’t need to use TLS on the internal port (usually 8003) unless you really need to open that up to the Internet i.e. simulators on remote machines will need to connect to your Robust services or you split services over multiple remote machines. Most of the rest of the Internet now uses HTTPS for almost everything, certainly for the Web, FTP, SSH, e-mail and so on. That bring me to a final observation: there are no TLS settings for the internal port in this situation, so you would still need to use Nginx as a reverse proxy for this. Correction: there is no separate setting but, when https_main = True and https_listener = True, both the private port and the https_port are served over HTTPS unless http_external is also set. Should this be documented more precisely? There is a use case for these settings existing in such a situation, although most people probably wouldn’t need to use them unless they anticipate running a public grid to which others can connect regions. It’s a bit problematic too if you want no HTTPS on the firewalled internal port (where there is no need for the encryption overhead) but you do want it on the public-facing port.

Configuring secure HTTPS ports with TLS (“SSL”) on OpenSim

Background

It has already been remarked in an earlier post that it is now possible to configure the simulator to use secure ports on OpenSim with TLS (still erroneously but commonly known by the name of its defunct predecessor SSL), i.e. that you can run it on HTTPS instead of HTTP. However, there is no native ability within OpenSim to do this for the ROBUST services, including most critically the login service. This means that your password details are broadcast in plain text at the time of login. Obviously this is far from ideal.

In order to provide secure ports it is necessary to configure a reverse proxy, of which the most obvious and commonly suggested by OpenSim administrators is Nginx, which also happens to be the best all-round modern HTTP(S) server and an improvement (in my opinion) on the venerable but battle-tested and dependable Apache. (See here for a discussion, in which it is stated that OSGrid uses Nginx.) For all this, there appears to be no published advice on how to achieve any of this. It seems no surprise that few – if any? – publicly available OpenSim servers on the Hypergrid seem to be configured to use HTTPS ports with TLS. It is fiddly, so this is worth providing here.

Most other server software in live installations is configured to use secure ports as an industry standard – why should OpenSim not follow the same standards? Otherwise I would suggest that you can never store personal data in OpenSim and you can never be sure of not being hacked. It’s fairly unlikely that an OpenSim grid would be an attractive target for a hacker, being somewhat niche, but it is entirely possible and no doubt has happened. (Famously, SL was hacked with flying penises.)

Secure ports 9002 and 9003 on Ocean Grid

Ocean Grid is now an example of just such a grid. In fact, for reasons that we shall come to later, it remains possible to log into Ocean Grid using the insecure HTTP port 8002. However, as of 2 May 2020 it is now also possible to use the secure HTTPS port 9002. Furthermore, the traffic to the private port is also configured on 9003 instead of 8003 for reasons specific to Ocean Grid that you may not need to bother with: if your internal port does not need to be open to the Internet then only your subnet will be able to see that traffic anyway, so why add the (fairly small) overhead of encryption?

First of all I began by configuring a second instance of ROBUST. Ocean Grid now runs duplicate copies of all the services. I have never separated, for example, the asset server from the others and I have not done so now either, but this can be done too. This would use Nginx as a reverse proxy for its other purpose, namely to load balance between duplicate copies of services, whether the whole lot of them in one ROBUST instance as I have done or on a service-by-service basis. The obvious one to do this with is the asset server. It depends on the ancient Tiny Web Server, written in C#, which is very slow and probably ought to be replaced – I’d suggest with h2o because it is fast and can do HTTP/2 and (experimentally so far) the new HTTP/3 (formerly QUIC) over UDP. So far I have configured no load balancing for Ocean Grid. One large 1280×1280 test region/simulator (Rheged) communicates by HTTPS while the other four regions (again, all on separate simulators to prevent out-of-memory crashes) all still use the original HTTP port. This of course may change in future.

In case you are wondering how I have different regions on different simulators, I have adapted Gwyn Llewelyn’s brilliant instructions on how to run multiple instances concurrently. Thanks, Gwyn ❤ (Be still, my virtual heart!) I also use some scripts that use GNU Screen to automatically switch between the console interfaces of the regions/simulators and ROBUST.

The upshot of all this is that all the services are available by either port. You can log in locally or via Hypergrid by either and reach the same simulators with no apparent difference in performance between the two. In fact, removing a region/simulator that is 5×5 larger than a normal region (i.e. 25 times as big) to a separate asset service has considerably improved performance. Otherwise there are only four 256×256 traditional regions in Ocean Grid to date.

It would of course be possible to attach other people’s regions on other servers to Ocean Grid, although this has not ever been done to date because it is a small private grid with mainly just myself, Starflower Bracken, as the principal user. I get a small number of Hypergrid visitors and a tiny number of visits from old friends of 2007 vintage who I met years ago in SL and have registered accounts locally on my grid. This would add a little more impetus to use HTTPS for security reasons, as the internal services then need to be open to the public Internet and there are more targets to attack. In any case, the same principles apply about best security practices as outlined above.

Before moving on to the mechanics of the installation, it suffices to add that there will be further tweaks as time goes on, probably including the load balancing described above in order to provide a much-needed boost to performance, especially as regards load on the asset server.

Problem with https:// prefix in the viewer

One particular tweak, migrating entirely to HTTPS and removing the insecure ports, will have to be has been postponed for an unknown period of some time. The grid selector in the viewer has always previously contained a bug [FIRE-24068 fixed 2020-11-07, SV-2392 fixed at unknown date], since it was first added to the original viewer for OpenSim purposes, that adds the http:// prefix to any loginURI and makes it impossible to add https:// instead. The only workaround to this annoying problem is to manually edit grids.user.xml (or grids.xml in some viewers). On doing this, HTTPS logins work perfectly, including using free Let’s Encrypt certificates as are installed on Ocean Grid. But less experienced users may not know how to edit this XML file, so any total migration would shut them out of logging in locally to the grid. Now that the major viewers allow this, it may make sense to migrate to the secure port, which is currently under review. You may ask, who cares since only I log in locally for the most part, while other visitors come via Hypergrid. In my case I have one reasonably frequent visitor who logs in with a locally registered account, who happens to be a very welcome one. I don’t really want to put a barrier in the way of the few local visits that I do still receive or force people to come via Hypergrid. If you do visit me via Hypergrid then I urge you to use port 9002 and thus to do so securely!

NOTE 2021-09-15, edited 2021-09-26: It is now possible to use Firestorm and Singularity with secure ports. (Singularity has a recent OpenSim version from 2020 despite being listed as an inactive viewer or in an “unknown” state – what is the status of this viewer? I was unable to run Dayturn 1.8.10 or 1.8.9 on Windows 10 as it simply failed to start for me, so I have not been able to test it. The VL Cool Viewer also supports HTTPS (although it will let you add the grid with the secure port OR the insecure port but not both under different names!) Radegast (text-only viewer) supports HTTPS. SceneGate (viewer with reduced functionality) supports HTTPS and for bonus points gives a security warning when connecting to insecure HTTP ports. This seems like a much more healthy position than described above. If Dayturn allows secure ports, there appears to be little good reason not to migrate entirely to secure ports, which I am seriously considering.

Setting up the ROBUST server with HTTPS

First of all you need to configure and run a second copy of ROBUST. I copied Robust.HG.ini to a new file Robust.HG.tls.ini and then edited that. You will use -inifile=”$DIR/Robust.HG.tls.ini” where you can replace $DIR with the path to wherever you keep the file, if you don’t use the method that I use.

Then you need to edit the following in blue, adapting it as appropriate for your purposes:

[Const]
BaseURL = “https://oceangrid.net”
PublicPort = “8102″
; The proxied external public port of the Robust server
PublicPort2 = “9002”
PrivatePort = “8103″

[ServiceList]
VoiceConnector = “9004/OpenSim.Server.Handlers.dll:FreeswitchServerConnector”

[Hypergrid]
HomeURI = “${Const|BaseURL}:${Const|PublicPort2}”
GatekeeperURI = “${Const|BaseURL}:${Const|PublicPort2}”

[LoginService]
MapTileURL = “${Const|BaseURL}:${Const|PublicPort2}/”;
SearchURL = “${Const|BaseURL}:${Const|PublicPort2}/”;
SRV_HomeURI = “${Const|BaseURL}:${Const|PublicPort2}”
SRV_InventoryServerURI = “${Const|BaseURL}:${Const|PublicPort2}”
SRV_AssetServerURI = “${Const|BaseURL}:${Const|PublicPort2}”
SRV_ProfileServerURI = “${Const|BaseURL}:${Const|PublicPort2}”
SRV_FriendsServerURI = “${Const|BaseURL}:${Const|PublicPort2}”
SRV_IMServerURI = “${Const|BaseURL}:${Const|PublicPort2}”
SRV_GroupsServerURI = “${Const|BaseURL}:${Const|PublicPort2}”

[GridInfoService]
login = ${Const|BaseURL}:${Const|PublicPort2}/
gridname = “Ocean Grid TLS
gridnick = “Ocean Grid TLS
gatekeeper = ${Const|BaseURL}:${Const|PublicPort2}/
uas = ${Const|BaseURL}:${Const|PublicPort2}/

In the case of OpenSim, there are cascading copies of OpenSim.ini in order to override certain settings for each region/simulator and inherit the rest of the settings from the main file. You may not have that setup, of course. However, this is what I did for the copy for my region Rheged:

[Const]
BaseHostname = “oceangrid.net”
BaseURL = https://${Const|BaseHostname}
PublicPort = “9002″
PrivURL = https://localhost
PrivatePort = “9003″
;; the following line was for testing – ignore
;PrivatePort = “8103”

Step required only if you are using port 9003 HTTPS on localhost

There is also another step required for making the certificates for localhost (or 127.0.0.1) work if, like me, you are making the internal services function over HTTPS. There are better ways to do this and this is a bit of a hack but bear in mind that the loss in security is fairly inconsequential since it is only on the internal subnet with only trusted devices connecting. As noted above, you don’t even need to encrypt these if they are never accessed from the public Internet but in my case they are because I have an external proxy server as well, which provides a roundabout solution to the lack of NAT loopback (NAT hairpinning) on the rather rubbish router that my ISP has provided. A better solution would be to get a decent router (and preferably a fixed IP address, as I used to have, rather than Dynamic DNS) and then I could just keep port 8003 internal and dispense with 9003. (I could alternatively use the /etc/hosts file on any other machine on the network running a viewer to connect with the local grid.) As also noted, another possible reason to expose these ports to the Internet is if external simulators are connecting.

Anyway, here is what I did:

[Startup]
; #
; # SSL certificates validation options
; #

; SSL certificate validation options
; you can allow selfsigned certificates or no official CA with next option set to true
; NoVerifyCertChain = true
NoVerifyCertChain = true
; you can also bypass the hostname or domain verification
; NoVerifyCertHostname = true
NoVerifyCertHostname = true
; having both options true does provide encryption but with low security
; set both true if you don’t care to use SSL, they are needed to contact regions or grids that do use it.

Setting up the simulator to use HTTPS (separate, optional step)

Again, for completeness, another step that is strictly not necessary is to give it a secure port. I actually did this some time ago quite, separately from all of this, for just the simulator rather than ROBUST:

[Network]
http_listener_port = 9106 ; if http_listener_ssl = true then this will be ignored

;; THIS IS EXPERIMENTAL IN OPENSIM 0.9.1.0
; ssl config: Experimental!
http_listener_ssl = true ; if set to true main server is replaced by a ssl one
http_listener_sslport = 9206 ; Use this port for SSL connections
; currently if using ssl, regions ExternalHostName must the the same and equal to http_listener_cn
; this will change is future
http_listener_cn = “oceangrid.net”
; if the cert doesnt have a official CA or is selfsigned viewers option NoVerifySSLCert need to be set true
http_listener_cert_path = “/opt/opensim/bin/certs/oceangrid.p12” ; path for the cert file that is valid for the ExternalHostName
http_listener_cert_pass = “your_password_here” ; the cert password

; the handler is in [opensim]/OpenSim/Server/Base/HttpServerBase.cs
http_listener_ssl_cert = “” ; as of 2019-10-11 this is not fetched by [opensim]/OpenSim/Framework/NetworkServersInfo.cs
; but the next undocumented lines are fetched, though who knows what, if anything, is done with them since it doesn’t
; work and you get the error “Error – certificate Parameter name: ‘certificate’ cannot be null.”

Nginx reverse proxy configuration

The next step is to provide the Nginx reverse proxy configuration as follows (tidied up a bit!) in a file called something like /etc/nginx/sites-available/oceangrid.net-9002-9003 as follows:

server {
listen 9002 ssl http2;
listen [::]:9002 ssl http2;

server_name oceangrid.net http://www.oceangrid.net;

ssl_session_cache shared:SSL:20m;
ssl_session_timeout 10m;

ssl_protocols TLSv1 TLSv1.1 TLSv1.2 TLSv1.3;
#very secure, very compatible
ssl_ciphers ECDH+AESGCM:ECDH+AES256:ECDH+AES128:DH+3DES:!ADH:!AECDH:!MD5;
#highly secure, less compatible
#ssl_ciphers ECDH+AESGCM:ECDH+AES256:ECDH+AES128:!ADH:!AECDH:!MD5;
ssl_prefer_server_ciphers on;

location / {
proxy_pass http://127.0.0.1:8102$1;
#resolver 8.8.8.8; #public Google IPv4 DNS resolver (insecure)
proxy_redirect off;
proxy_buffering off;
proxy_set_header Host $host:$server_port;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header X-Forwarded-Proto $scheme;
}

location ~ \.php$ {
proxy_pass http://127.0.0.1:8102$1;
#resolver 8.8.8.8; #public Google IPv4 DNS resolver (insecure)
proxy_redirect off;
proxy_buffering off;;
proxy_set_header Host $host:$server_port;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header X-Forwarded-Proto $scheme;
}

access_log /var/log/nginx/grid.oceangrid.access.log;
error_log /var/log/nginx/grid.oceangrid.error.log;

ssl_certificate /etc/letsencrypt/live/www.oceangrid.net/fullchain.pem; # managed by Certbot
ssl_certificate_key /etc/letsencrypt/live/www.oceangrid.net/privkey.pem; # managed by Certbot

}

server {
listen 9003 ssl http2;
listen [::]:9003 ssl http2;

server_name oceangrid.net http://www.oceangrid.net;

ssl_session_cache shared:SSL:20m;
ssl_session_timeout 10m;

ssl_protocols TLSv1 TLSv1.1 TLSv1.2 TLSv1.3;
#very secure, very compatible
ssl_ciphers ECDH+AESGCM:ECDH+AES256:ECDH+AES128:DH+3DES:!ADH:!AECDH:!MD5;
#highly secure, less compatible
#ssl_ciphers ECDH+AESGCM:ECDH+AES256:ECDH+AES128:!ADH:!AECDH:!MD5;
ssl_prefer_server_ciphers on;

location / {
proxy_pass http://127.0.0.1:8103$1;
#resolver 8.8.8.8; #public Google IPv4 DNS resolver (insecure)
proxy_redirect off;
proxy_buffering off;
proxy_set_header Host $host:$server_port;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header X-Forwarded-Proto $scheme;
}

location ~ \.php$ {
proxy_pass http://127.0.0.1:8103$1;
#resolver 8.8.8.8; #public Google IPv4 DNS resolver (insecure)
proxy_redirect off;
proxy_buffering off;
proxy_set_header Host $host:$server_port;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header X-Forwarded-Proto $scheme;
}

access_log /var/log/nginx/grid.oceangrid.access.log;
error_log /var/log/nginx/grid.oceangrid.error.log;

ssl_certificate /etc/letsencrypt/live/www.oceangrid.net/fullchain.pem; # managed by Certbot
ssl_certificate_key /etc/letsencrypt/live/www.oceangrid.net/privkey.pem; # managed by Certbot

}

Finally make another copy of this file, for example called /etc/nginx/sites-available/localhost-9002-9002 but comment out (#) the lines that are your equivalent of server_name oceangrid.net; near the top. These will then work for localhost (127.0.0.1) on those ports. You will now need to type:

sudo ln -s /etc/nginx/sites-available/localhost-9002-9002 /etc/nginx/sites-enabled/localhost-9002-9003
sudo ln -s /etc/nginx/sites-available/oceangrid.net-9002-9003 /etc/nginx/sites-enabled/oceangrid.net-9002-9003
sudo systemctl restart nginx
OR
sudo service nginx restart

Here you have it. As discussed above, you won’t need to do the localhost part if 8003 is firewalled on your local network, in which case you will not be using 9003 and those sections can be ignored here in both files.

Bear in mind that the resolver setting may be different on different servers and I must leave you to discover the best and safest way to do this on your own configuration – don’t use an easily guessable public DNS resolver like the one commented out above because of the risk of interception.

The future of HTTPS in the open metaverse

You could adapt and simply these instructions easily enough for a standalone installation of OpenSim but, since I don’t use one, unless somebody contacts me for advice then I shall leave it to them to do so because I don’t see it should be too horribly difficult based on the instructions for a grid. Most people’s requirements will be simpler than mine but my grid has evolved over almost 10 years.

I hope that people use these instructions. I am asking people to adopt 9002 and 9003 for these secure ports, i.e. to establish a convention that is easily guessable like the present 8002 and 8003 convention. Please also add your voice to the call to fix the grid selector in the various viewers [FIRE-24068SV-2392]. I am looking forward to a more secure open metaverse in the future and hope I have contributed to that.