OAuth2 Proxy

OAuth2 Proxy is a reverse proxy that signs users in with an OIDC provider before they reach your application. It can also act as the forward-auth endpoint of Nginx, Caddy, or Traefik. With Casdoor as the provider, you can let in only the members of a Casdoor group or the users who hold a Casdoor role.

The configuration on this page was tested end to end with OAuth2 Proxy v7.15 and Casdoor v4.17.

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If you only need Casdoor sign-in in front of an application and don't need OAuth2 Proxy itself, casdoor-forward-auth does the same job for Traefik, Caddy, and Nginx, and passes the user's groups and roles in request headers.

Step 1: Create the application in Casdoor

1. In the organization of your users, add an application (or open an existing one).

2. Add the callback of OAuth2 Proxy to Redirect URLs:

   https://app.example.com/oauth2/callback

3. On the OIDC/OAuth tab, set:

   • Token format: JWT-Standard
   • Token group format: Name (group), so groups arrive as devs instead of my-org/devs

4. Save, and note the Client ID and Client secret.

Why JWT-Standard: with the default JWT format, a user whose email is not verified can't sign in (OAuth2 Proxy rejects email_verified: false, and users created by an administrator usually have an unverified email), and the roles claim holds whole role objects instead of role names. See What Casdoor sends.

Step 2: Configure OAuth2 Proxy

Create oauth2-proxy.cfg:

provider = "oidc"
oidc_issuer_url = "https://door.example.com"
client_id = "<client ID>"
client_secret = "<client secret>"
redirect_url = "https://app.example.com/oauth2/callback"
scope = "openid email profile"
email_domains = ["*"]

cookie_secret = "<random secret>"
http_address = "0.0.0.0:4180"
upstreams = ["http://127.0.0.1:8080"]

# Let in only members of the Casdoor group "devs"
oidc_groups_claim = "groups"
allowed_groups = ["devs"]

• oidc_issuer_url is the URL of Casdoor, without a trailing slash. It must be exactly the issuer shown at https://door.example.com/.well-known/openid-configuration. Casdoor builds the issuer from origin in conf/app.conf, or from the request's host when origin is empty; if the two differ, OAuth2 Proxy fails with issuer did not match.
• cookie_secret must be 16, 24, or 32 bytes, for example the output of openssl rand -base64 32 | tr -- '+/' '-_'.
• Keep the profile scope: Casdoor returns groups and roles from its userinfo endpoint only when profile is granted.
• upstreams is your application.

Start it:

oauth2-proxy --config oauth2-proxy.cfg

Open https://app.example.com. After signing in to Casdoor, members of devs reach the application and everyone else gets 403 Forbidden.

Restrict access by role instead

To check a Casdoor role instead of a group, read the roles claim:

oidc_groups_claim = "roles"
allowed_groups = ["admin"]

allowed_groups then holds role names, without the organization.

Check what OAuth2 Proxy received

After signing in, open https://app.example.com/oauth2/userinfo. It shows the groups OAuth2 Proxy extracted:

{"user":"d1a5f427-...","email":"alice@example.com","groups":["devs"],"preferredUsername":"alice"}

If groups is empty, the user has no group or role in Casdoor, or the claim name is wrong. If it contains long JSON strings like {"owner":"my-org","name":"admin",...}, the application still uses the default JWT format with oidc_groups_claim = "roles"; switch the format to JWT-Standard.

What Casdoor sends

How the user's groups and roles reach OAuth2 Proxy depends on the application's Token format:

Token format	groups	roles	Unverified email
JWT-Standard	from userinfo, group names	from userinfo, role names	signs in
JWT-Custom	in the token if Groups is in Token fields	in the token if you add a token attribute roles (see below)	signs in
JWT (default)	in the token	role objects, not usable for allowed_groups	rejected
JWT-Empty	in the token	from userinfo, role names	signs in

With JWT-Standard, the token itself carries only standard OIDC claims. OAuth2 Proxy looks up any claim that is missing from the token at Casdoor's userinfo endpoint, so groups and roles still arrive, once per sign-in.

Token group format controls the group values in all formats: ID (default) gives my-org/devs, Name gives devs, and Path gives my-org/parent/devs for nested groups.

To put role names into the token itself, use JWT-Custom and add a row to Token attributes:

Name	Category	Value	Type
roles	Existing Field	Roles	Array

If Token fields is not empty, it also limits what the userinfo endpoint returns (see Token fields). Include Groups (and Roles when you read roles from userinfo), or leave it empty.

If you must keep the default JWT format, add insecure_oidc_allow_unverified_email = true so users with an unverified email can sign in, and restrict by groups only.

Pass the user to your application

OAuth2 Proxy adds these headers to requests it forwards (pass_user_headers, on by default):

Header	Value
X-Forwarded-User	Casdoor user ID (the sub claim)
X-Forwarded-Preferred-Username	Casdoor user name, e.g. alice
X-Forwarded-Email	Email address
X-Forwarded-Groups	Groups (or roles), comma separated

Make sure your application is only reachable through OAuth2 Proxy, otherwise anyone can send these headers directly.

To use OAuth2 Proxy as the forward-auth endpoint of Nginx (auth_request), Caddy (forward_auth), or Traefik (forwardAuth) instead of as a reverse proxy, point the proxy at its /oauth2/auth endpoint; see Integrations in the OAuth2 Proxy documentation.

Troubleshooting

Symptom	Cause and fix
issuer did not match the issuer returned by provider at startup	oidc_issuer_url differs from the issuer in Casdoor's discovery document. Set origin in Casdoor's conf/app.conf to its public URL and use the same value here.
500 after sign-in, log says email in id_token ... isn't verified	The application uses the default JWT format and the user's email is not verified. Switch to JWT-Standard, or set insecure_oidc_allow_unverified_email = true.
403 Forbidden after sign-in	The user is not in allowed_groups. Open /oauth2/userinfo to see what OAuth2 Proxy received and compare it with Token group format.
Casdoor shows Redirect URI: ... doesn't exist in the allowed Redirect URI list	Add https://app.example.com/oauth2/callback to the application's Redirect URLs.