Requesting a client certificate from a remote Vault server with Microsoft Entra ID authentication

This guide shows how an administrator configures the Vault OIDC authentication method with Microsoft Entra ID as the identity provider, and how a user logs in with the Entra ID account to a remote Vault server and gets a client certificate signed by the Vault CA.

Prerequisites

The Vault PKI configured as described in step 1a of the main README.md: the pki_int mount and the wif-client role (vault_configure.sh).
A Vault server reachable over HTTPS. The examples use https://vault.koszewscy.waw.pl.
Permissions to register applications in the Entra ID tenant.
vault and openssl on the workstation of the administrator and of the user, and a web browser on the workstation of the user.

The commands are written for bash.

1. Register the application in Entra ID

Role: Administrator

Register an application for Vault in the tenant.
Add the redirect URIs of the type "Web":
- http://localhost:8250/oidc/callback for the CLI login.
- https://vault.koszewscy.waw.pl/ui/vault/auth/oidc/oidc/callback for the Vault UI login.
Record the Application (client) ID and the Directory (tenant) ID.
Under Certificates & secrets, create a client secret and record its value.
Under Token configuration, select Add groups claim, select the group types to include (Security groups), and under Customize token properties by type select Group ID in the ID section. The groups claim of the ID token then contains the object IDs of the groups of the user.
Create a security group of the users who may request certificates, add the users to it, and record the Object ID of the group.
Under API permissions, add the Microsoft Graph delegated permission User.Read and grant the admin consent. Entra ID omits the groups from the token of users who are members of more than 200 groups, and Vault then reads them through Graph.

2. Configure Vault

Role: Administrator

Point the CLI at the server and authenticate with an administrator token:

export VAULT_ADDR=https://vault.koszewscy.waw.pl
export VAULT_TOKEN=<admin-token>

Create a policy that allows signing certificate requests with the wif-client role and nothing else.
Enable the OIDC authentication method and configure Entra ID as the provider.
Create a role that accepts only members of the group and attaches the policy. The token is valid for 15 minutes and can be renewed up to 1 hour.

pki-client.hcl:

path "pki_int/sign/wif-client" {
  capabilities = ["update"]
}

oidc-config.json:

{
  "oidc_discovery_url": "https://login.microsoftonline.com/<tenant-id>/v2.0",
  "oidc_client_id": "<client-id>",
  "oidc_client_secret": "<client-secret>",
  "default_role": "entra-pki",
  "provider_config": {
    "provider": "azure"
  }
}

oidc-role.json:

{
  "role_type": "oidc",
  "user_claim": "sub",
  "allowed_redirect_uris": [
    "http://localhost:8250/oidc/callback",
    "https://vault.koszewscy.waw.pl/ui/vault/auth/oidc/oidc/callback"
  ],
  "groups_claim": "groups",
  "oidc_scopes": ["profile"],
  "bound_claims": {"groups": ["<group-object-id>"]},
  "token_policies": ["pki-client"],
  "token_ttl": "15m",
  "token_max_ttl": "1h"
}

vault policy write pki-client pki-client.hcl

vault auth enable oidc

vault write auth/oidc/config @oidc-config.json

vault write auth/oidc/role/entra-pki @oidc-role.json

Delete oidc-config.json after the configuration is written, because it contains the client secret.

The redirect URIs in the role must match the ones registered in Entra ID exactly, including the scheme, the port and the trailing path. The bound_claims entry limits the login to the members of the group, the other Entra ID users get an error at login.

The CLI cannot express the bound_claims map as key=value arguments, which is why the configuration is read from JSON files.

Note: The wif-client role accepts any common name (allow_any_name=true). Every member of the group can therefore request a certificate with any subject CN, including the CN that other users or workloads rely on as the WiF subject. Restrict the role (allowed_domains, allow_bare_domains, enforce_hostnames) when the users must not choose their CN freely.

3. Request a certificate

Role: User

Set the address of the Vault server. Set VAULT_CACERT as well when the server certificate is issued by a private CA.
```
export VAULT_ADDR=https://vault.koszewscy.waw.pl
export VAULT_CACERT=/path/to/server-ca.pem
```
Unset VAULT_TOKEN, because a token in this environment variable takes precedence over the token stored by vault login and the CLI would keep using it. Then log in with the Entra ID account. The skip_browser=true parameter stops the CLI from launching the browser. The CLI prints the Entra ID sign-in link instead, waits on localhost:8250 for the redirect, and after the sign-in stores the token in the token helper file (~/.vault-token).
```
unset VAULT_TOKEN
vault login -method=oidc skip_browser=true role=entra-pki
```
Open the printed link in the browser, or in the browser profile or the private window, signed in with the account that is a member of the group. Entra ID signs in with the session that the browser already has, without asking. A token of another account fails with claim "groups" does not match any associated bound claim values, because that account is not a member of the group.

The optional callbackhost, callbackport, listenaddress and mount parameters change the callback listener. The redirect URI built from them must be registered in Entra ID and listed in allowed_redirect_uris of the role.

Generate the client key and the CSR locally. The key is never sent to Vault.

openssl req \
    -newkey rsa:4096 \
    -keyout client_key.pem \
    -noenc \
    -subj "/CN=test-client" \
    -out client.csr

Sign the CSR with the Vault CA.

vault write -field=certificate pki_int/sign/wif-client \
    csr=@client.csr \
    common_name=test-client \
    ttl=8760h > client_cert.pem

Check the certificate.

openssl x509 -in client_cert.pem -noout -subject -issuer -dates -ext extendedKeyUsage

Revoke the token when the work is done.
```
vault token revoke -self
```

The user token can only sign with the wif-client role. Reading the role or any other path returns permission denied.

Next steps

Create the credentials configuration cred.json for client_cert.pem and client_key.pem. The names come from env.sh.

gcloud iam workload-identity-pools create-cred-config \
    "projects/${PROJECT_NUMBER}/locations/global/workloadIdentityPools/${POOL_ID}/providers/${PROVIDER_ID}" \
    --service-account="${SA_EMAIL}" \
    --credential-cert-path=client_cert.pem \
    --credential-cert-private-key-path=client_key.pem \
    --output-file=cred.json

Activate the service account with gcloud auth login --cred-file=cred.json.
Run the WIF tests.

Example test commands are in test_wif.sh.

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