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GitHub Action edited this page Feb 23, 2024 · 40 revisions

The preferred way to configure openvpn-auth-oauth2 is via environment variables. If you install the openvpn-auth-auth2 via Linux package, use the file /etc/sysconfig/openvpn-auth-oauth2 to configure openvpn-auth-oauth2.

Full configuration example

Configuration openvpn-auth-oauth2 for zitadel

# Define the public http endpoint here.
CONFIG_HTTP_BASEURL=http://<vpn>:9000/
CONFIG_HTTP_LISTEN=:9000
# Define a random value with 16 or 24 characters
CONFIG_HTTP_SECRET=1jd93h5b6s82lf03jh5b2hf9
CONFIG_OPENVPN_ADDR=unix:///run/openvpn/server.sock
CONFIG_OPENVPN_PASSWORD=<password from /etc/openvpn/password.txt>
CONFIG_OAUTH2_ISSUER=https://company.zitadel.cloud
CONFIG_OAUTH2_SCOPES=openid profile email offline_access
CONFIG_OAUTH2_CLIENT_ID=34372461928374612@any
CONFIG_OAUTH2_CLIENT_SECRET=ASDhjgadjhAUYSDGjkhasgdIATWDGJHASDtiwGDJAHSGDutwqdygASJKD12hfva

Configuration file

openvpn-auth-oauth2 supports configuration via a YAML file. The file can be passed via the --config flag.

Example 
debug:
    pprof: false
    listen: :9001
http:
    baseurl: "http://localhost:9000/"
    cert: ""
    check:
        ipaddr: false
    enable-proxy-headers: true
    key: ""
    listen: ":9000"
    # secret: ""
    # template: "" # Path to a HTML file which is displayed at the end of the screen
    tls: false
log:
    format: console
    level: INFO
oauth2:
    authorize-params: "a=c"
    client:
        id: "test"
        secret: "test"
    endpoint:
        # discovery: "https://idp/.well-known/openid-configuration"
        # auth: "https://idp/oauth/auth"
        # token: "https://idp/oauth/token"
    issuer: "https://idp"
    # provider: "generic"
    # scopes:
    #  - "openid"
    #  - "profile"
    validate:
        acr:
        #  - "phr"
        #  - "phrh"
        common-name: ""
        common-name-case-sensitive: false
        # groups:
        #  - "test"
        #  - "test2"
        # roles:
        #   - "test"
        #   - "test2"
        ipaddr: false
        issuer: true
    nonce: true
    pkce: true
    auth-style: "AuthStyleInParams"
    refresh:
        enabled: false
        expires: 8h0m0s
        # secret: ""
openvpn:
    addr: "unix:///run/openvpn/server.sock"
    auth-token-user: true
    auth-pending-timeout: 2m
    bypass:
        # common-names:
        # - "test"
        # - "test2"
    common-name:
        environment-variable-name: common_name
        mode: plain
    # password: ""
    pass-through:
        address: "unix:///run/openvpn/pass-through.sock"
        enabled: false
        # password: ""
        # socket-group: ""
        # socket-mode: 660
provider:
    google:
        admin-email: ""
        impersonate-account: ""
        service-account-config: ""

Supported configuration properties

Usage of openvpn-auth-oauth2:

  --config string
    	path to one .yaml config file (env: CONFIG_CONFIG)
  --debug.listen string
    	listen address for go profiling endpoint (env: CONFIG_DEBUG_LISTEN) (default ":9001")
  --debug.pprof
    	Enables go profiling endpoint. This should be never exposed. (env: CONFIG_DEBUG_PPROF)
  --http.baseurl string
    	listen addr for client listener (env: CONFIG_HTTP_BASEURL) (default "http://localhost:9000")
  --http.cert string
    	Path to tls server certificate (env: CONFIG_HTTP_CERT)
  --http.check.ipaddr
    	Check if client IP in http and VPN is equal (env: CONFIG_HTTP_CHECK_IPADDR)
  --http.enable-proxy-headers
    	Use X-Forward-For http header for client ips (env: CONFIG_HTTP_ENABLE__PROXY__HEADERS)
  --http.key string
    	Path to tls server key (env: CONFIG_HTTP_KEY)
  --http.listen string
    	listen addr for client listener (env: CONFIG_HTTP_LISTEN) (default ":9000")
  --http.secret value
    	Random generated secret for cookie encryption. Must be 16, 24 or 32 characters. If argument starts with file:// it reads the secret from a file. (env: CONFIG_HTTP_SECRET)
  --http.template string
    	Path to a HTML file which is displayed at the end of the screen (env: CONFIG_HTTP_TEMPLATE)
  --http.tls
    	enable TLS listener (env: CONFIG_HTTP_TLS)
  --log.format string
    	log format. json or console (env: CONFIG_LOG_FORMAT) (default "console")
  --log.level value
    	log level (env: CONFIG_LOG_LEVEL) (default INFO)
  --oauth2.auth-style value
    	Auth style represents how requests for tokens are authenticated to the server. Possible values: AuthStyleAutoDetect, AuthStyleInParams, AuthStyleInHeader. See https://pkg.go.dev/golang.org/x/oauth2#AuthStyle (env: CONFIG_OAUTH2_AUTH__STYLE) (default AuthStyleInParams)
  --oauth2.authorize-params string
    	additional url query parameter to authorize endpoint (env: CONFIG_OAUTH2_AUTHORIZE__PARAMS)
  --oauth2.client.id string
    	oauth2 client id (env: CONFIG_OAUTH2_CLIENT_ID)
  --oauth2.client.secret value
    	oauth2 client secret. If argument starts with file:// it reads the secret from a file. (env: CONFIG_OAUTH2_CLIENT_SECRET)
  --oauth2.endpoint.auth string
    	custom oauth2 auth endpoint (env: CONFIG_OAUTH2_ENDPOINT_AUTH)
  --oauth2.endpoint.discovery string
    	custom oauth2 discovery url (env: CONFIG_OAUTH2_ENDPOINT_DISCOVERY)
  --oauth2.endpoint.token string
    	custom oauth2 token endpoint (env: CONFIG_OAUTH2_ENDPOINT_TOKEN)
  --oauth2.issuer string
    	oauth2 issuer (env: CONFIG_OAUTH2_ISSUER)
  --oauth2.nonce
    	If true, a nonce will be defined on the auth URL which is expected inside the token. (env: CONFIG_OAUTH2_NONCE) (default true)
  --oauth2.pkce
    	If true, Proof Key for Code Exchange (PKCE) RFC 7636 is used for token exchange. (env: CONFIG_OAUTH2_PKCE) (default true)
  --oauth2.provider string
    	oauth2 provider (env: CONFIG_OAUTH2_PROVIDER) (default "generic")
  --oauth2.refresh.enabled
    	If true, openvpn-auth-oauth2 stores refresh tokens and will use it do an non-interaction reauth. (env: CONFIG_OAUTH2_REFRESH_ENABLED)
  --oauth2.refresh.expires duration
    	TTL of stored oauth2 token. (env: CONFIG_OAUTH2_REFRESH_EXPIRES) (default 8h0m0s)
  --oauth2.refresh.secret value
    	Required, if oauth2.refresh.enabled=true. Random generated secret for token encryption. Must be 16, 24 or 32 characters. If argument starts with file:// it reads the secret from a file. (env: CONFIG_OAUTH2_REFRESH_SECRET)
  --oauth2.scopes value
    	oauth2 token scopes. Defaults depends on oauth2.provider. Comma separated list. Example: openid,profile,email (env: CONFIG_OAUTH2_SCOPES)
  --oauth2.validate.acr value
    	oauth2 required acr values. Comma separated list. Example: phr,phrh (env: CONFIG_OAUTH2_VALIDATE_ACR)
  --oauth2.validate.common-name string
    	validate common_name from OpenVPN with IDToken claim. For example: preferred_username or sub (env: CONFIG_OAUTH2_VALIDATE_COMMON__NAME)
  --oauth2.validate.common-name-case-sensitive
    	If true, openvpn-auth-oauth2 will validate the common case in sensitive mode (env: CONFIG_OAUTH2_VALIDATE_COMMON__NAME__CASE__SENSITIVE)
  --oauth2.validate.groups value
    	oauth2 required user groups. If multiple groups are configured, the user needs to be least in one group. Comma separated list. Example: group1,group2,group3 (env: CONFIG_OAUTH2_VALIDATE_GROUPS)
  --oauth2.validate.ipaddr
    	validate client ipaddr between VPN and oidc token (env: CONFIG_OAUTH2_VALIDATE_IPADDR)
  --oauth2.validate.issuer
    	validate issuer from oidc discovery (env: CONFIG_OAUTH2_VALIDATE_ISSUER) (default true)
  --oauth2.validate.roles value
    	oauth2 required user roles. If multiple role are configured, the user needs to be least in one role. Comma separated list. Example: role1,role2,role3 (env: CONFIG_OAUTH2_VALIDATE_ROLES)
  --openvpn.addr string
    	openvpn management interface addr. Must start with unix:// or tcp:// (env: CONFIG_OPENVPN_ADDR) (default "unix:/run/openvpn/server.sock")
  --openvpn.auth-pending-timeout duration
    	How long OpenVPN server wait until user is authenticated (env: CONFIG_OPENVPN_AUTH__PENDING__TIMEOUT) (default 3m0s)
  --openvpn.auth-token-user
    	Define auth-token-user for all sessions (env: CONFIG_OPENVPN_AUTH__TOKEN__USER) (default true)
  --openvpn.bypass.common-names value
    	bypass oauth authentication for CNs. Comma separated list. (env: CONFIG_OPENVPN_BYPASS_COMMON__NAMES)
  --openvpn.common-name.environment-variable string
    	Name of the environment variable in the OpenVPN management interface which contains the common name. If username-as-common-name is enabled, this should be set to 'username' to use the username as common name. Other values like 'X509_0_emailAddress' are supported. See https://openvpn.net/community-resources/reference-manual-for-openvpn-2-6/#environmental-variables for more information. (env: CONFIG_OPENVPN_COMMON__NAME_ENVIRONMENT__VARIABLE) (default "common_name")
  --openvpn.common-name.mode value
    	If common names are too long, use md5/sha1 to hash them or omit to skip them. If omit, oauth2.validate.common-name does not work anymore. Values: [plain,omit] (env: CONFIG_OPENVPN_COMMON__NAME_MODE) (default plain)
  --openvpn.pass-through.address string
    	The address of the pass-through socket. Must start with unix:// or tcp:// (env: CONFIG_OPENVPN_PASS__THROUGH_ADDRESS) (default "unix:/run/openvpn-auth-oauth2/server.sock")
  --openvpn.pass-through.enabled
    	If true, openvpn-auth-oauth2 will setup a pass-through socket for the OpenVPN management interface.  (env: CONFIG_OPENVPN_PASS__THROUGH_ENABLED)
  --openvpn.pass-through.password value
    	The password for the pass-through socket. If argument starts with file:// it reads the secret from a file. (env: CONFIG_OPENVPN_PASS__THROUGH_PASSWORD)
  --openvpn.pass-through.socket-group string
    	The group for the pass-through socket. Used only, if openvpn.pass-through.address starts with unix:// If empty, the group of the process is used. (env: CONFIG_OPENVPN_PASS__THROUGH_SOCKET__GROUP)
  --openvpn.pass-through.socket-mode uint
    	The unix file permission mode for the pass-through socket. Used only, if openvpn.pass-through.address starts with unix:// (env: CONFIG_OPENVPN_PASS__THROUGH_SOCKET__MODE) (default 660)
  --openvpn.password value
    	openvpn management interface password. If argument starts with file:// it reads the secret from a file. (env: CONFIG_OPENVPN_PASSWORD)
  --provider.google.admin-email string
    	Admin email for service account to impersonate for google admin api. Used, if oauth2.validate.groups is set. (env: CONFIG_PROVIDER_GOOGLE_ADMIN__EMAIL)
  --provider.google.impersonate-account string
    	Service account to impersonate if Default Application Credentials used. Used, if oauth2.validate.groups is set. (env: CONFIG_PROVIDER_GOOGLE_IMPERSONATE__ACCOUNT)
  --provider.google.service-account-config value
    	Path to service account config for google admin api. Required, if oauth2.validate.groups is set. If argument starts with file:// it reads the secret from a file. (env: CONFIG_PROVIDER_GOOGLE_SERVICE__ACCOUNT__CONFIG)
  --version
    	show version

Read sensitive data from file

The following parameter supports sensitive data from the file:

  • http.secret
  • openvpn.password
  • oauth2.client.secret
  • oauth2.refresh.secret

To read the sensitive data from the file, use the file:// prefix, e.g. file://path/to/secret.txt.

Configuration openvpn-auth-oauth2

openvpn-auth-oauth2 starts an HTTP listener which needs to be accessible from the OpenVPN client before the VPN connection is established. By default, the http listener runs on :9000.

It'd highly recommend putting openvpn-auth-oauth2 behind a reverse proxy which terminates the TLS connections. It's important to configure CONFIG_HTTP_BASE_URL because openvpn-auth-oauth2 need to know the redirect url.

Example:

# openvpn-auth-oauth2 config file
CONFIG_HTTP_LISTEN=:9000
CONFIG_HTTP_BASE_URL=https://login.example.com

Filesystem Permissions

When started by systemd, openvpn runs with a dynamic arbitrary UID. This means that it may not have access to certain files and directories if the appropriate permissions are not set.

Any additional files, such as TLS keys, should be placed under the /etc/openvpn-auth-oauth2/ directory. The owner of these files should be root and the group should be openvpn-auth-oauth2. This ensures that openvpn has the necessary permissions to access and use these files.

When installing the openvpn-auth-oauth2 Linux package, it will automatically handle the creation of the openvpn-auth-oauth2 system group. This group is used to manage access to the necessary files and directories and should be used to manage the permissions of any additional files.

Setup OpenVPN server

To connect openvpn-auth-oauth2 with openvpn server, add lines below:

# openvpn server.conf
...
# /etc/openvpn/password.txt is a password file where the password must be on first line
management /run/openvpn/server.sock unix /etc/openvpn/password.txt
management-client-auth
# management-hold holds the OpenVPN server until openvpn-auth-oauth2 has been connected.
# In some situation, there is a deadlock where systemd waits for OpenVPN server, not starting
#management-hold

# If auth-user-pass-optional is not set, the OpenVPN server requires username/password from clients
# and terminate the connection with an TLS error, if the client does not provide it.
auth-user-pass-optional
# openvpn-auth-oauth2 config file
CONFIG_OPENVPN_ADDR=unix:///run/openvpn/server.sock
CONFIG_OPENVPN_PASSWORD=<password>

Setup OIDC Provider

See Providers for more information

HTTPS Listener

Important

Remember to set CONFIG_HTTP_BASEURL correctly. It should start with https:// following your public domain name plus port.

Some SSO Provider like Entra ID requires https:// based redirect URL. In the default configuration, openvpn-auth-oauth2 listen on http://. There are two common ways to set up an HTTPS listener

Reverse proxy (nginx, traefik)

You can use one of your favorite http reverse proxies. Configure HTTPS on reverse proxy and proxy to an HTTP instance of openvpn-auth-oauth2. For beginners, traefik is recommended since it natively supports Let's Encrypt where you can get public SSL certificates for free.

Using native HTTPS support

openvpn-auth-oauth2 supports HTTPS out of the box.

CONFIG_HTTP_TLS=true
CONFIG_HTTP_KEY=server.key
CONFIG_HTTP_CERT=server.crt

To set up a self-signed certificate, you can use the command below:

export DOMAIN_NAME=vpn.example.com
openssl req -x509 -newkey rsa:4096 -sha256 -days 3650 -nodes -keyout server.key -out server.crt -subj "/CN=$DOMAIN_NAME" -addext "subjectAltName=DNS:$DOMAIN_NAME"

Non-interactive session refresh

With default settings, openvpn-auth-oauth2 does not store any tokens from the users. This requires an interactive login from user on each authentication, included on TLS soft-resets (if reneg-sec is triggered).

The interactive login can be avoided by requesting refresh tokens (via oauth2 scope offline_access; enabled by default) and store the token inside openvpn-auth-oauth2.

If enabled (via --oauth2.refresh.enabled=true), openvpn-auth-oauth2 will store the oauth2 refresh token in an in-memory key-value store. openvpn-auth-oauth2 is using AES to encrypt the tokens. The token will be bound to the OpenVPN client ID. While on initially connect the interactive login is still mandatory, openvpn-auth-oauth2 tries to initiate a non-interactive login with the refresh token against the OIDC provider and fallbacks to interactive login, if unsuccessful.

References:

CONFIG_OAUTH2_REFRESH_ENABLED=true
CONFIG_OAUTH2_REFRESH_EXPIRES=8h
CONFIG_OAUTH2_REFRESH_SECRET= # a static secret to encrypt token. Must be 16, 24 or 32

username-as-common-name

If username-as-common-name is configured at OpenVPN server, ensure that openvpn.common-name.environment-variable-name is set to username as well.

This is mandatory, because username-as-common-name works after the authentication process.

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