Use Azure AD for OIDC authentication

Note: Azure Active Directory Applications that have custom signing keys as a result of using the claims-mapping feature are currently not supported for OIDC authentication.

Reference: Azure Active Directory v2.0 and the OpenID Connect protocol

Choose your Azure tenant.
Go to Azure Active Directory and register an application for Vault.
Add Redirect URIs with the "Web" type. You may include two redirect URIs, one for CLI access another one for Vault UI access.
- http://localhost:8250/oidc/callback
- https://hostname:port_number/ui/vault/auth/oidc/oidc/callback
Record the "Application (client) ID" as you will need it as the oidc_client_id.
Under Endpoints, copy the OpenID Connect metadata document URL, omitting the /well-known... portion.
- The endpoint URL (oidc_discovery_url) will look like: https://login.microsoftonline.com/tenant-guid-dead-beef-aaaa-aaaa/v2.0
Under Certificates & secrets, add a client secret Record the secret's value as you will need it as the oidc_client_secret for Vault.

Connect AD group with Vault external group

Reference: Azure Active Directory with OIDC Auth Method and External Groups

To connect the AD group with a Vault external groups, you will need Azure AD v2.0 endpoints. You should set up a Vault policy for the Azure AD group to use.

Go to Azure Active Directory and choose your Vault application.
Go to Token configuration and Add groups claim. Select "All" or "SecurityGroup" based on which groups for a user you want returned in the claim.
In Vault, enable the OIDC auth method.

Configure the OIDC auth method with the oidc_client_id (application ID), oidc_client_secret (client secret), and oidc_discovery_url (endpoint URL) you recorded from Azure.

vault write auth/oidc/config \
   oidc_client_id="your_client_id" \
   oidc_client_secret="your_client_secret" \
   default_role="your_default_role" \
   oidc_discovery_url="https://login.microsoftonline.com/tenant_id/v2.0"

Configure the OIDC Role with the following:

user_claim should be "sub" or "oid" following the recommendation from Azure.
allowed_redirect_uris should be the two redirect URIs for Vault CLI and UI access.
groups_claim should be set to "groups".

oidc_scopes should be set to "https://graph.microsoft.com/.default profile".

vault write auth/oidc/role/your_default_role \
   user_claim="sub" \
   allowed_redirect_uris="http://localhost:8250/oidc/callback,https://online_version_hostname:port_number/ui/vault/auth/oidc/oidc/callback"  \
   groups_claim="groups" \
   oidc_scopes="https://graph.microsoft.com/.default profile" \
   policies=default

In Vault, create the external group. Record the group ID as you will need it for the group alias.
From Vault, retrieve the OIDC accessor ID from the OIDC auth method as you will need it for the group alias's mount_accessor.
Go to the Azure AD Group you want to attach to Vault's external group. Record the objectId as you will need it as the group alias name in Vault.

In Vault, create a group alias for the external group and set the objectId as the group alias name.

vault write identity/group-alias \
   name="your_ad_group_object_id" \
   mount_accessor="vault_oidc_accessor_id" \
   canonical_id="vault_external_group_id"

Optional azure-specific configuration

If a user is a member of more than 200 groups (directly or indirectly), Azure will send _claim_names and _claim_sources. For example, returned claims might look like:

{
  "_claim_names": {
    "groups": "src1"
  },
  "_claim_sources": {
    "src1": {
      "endpoint": "https://graph.windows.net...."
    }
  }
}

The OIDC auth method role can be configured to include the user ID in the endpoint URL, which will be used by Vault to retrieve the groups for the user. Additional API permissions must be added to the Azure app in order to request the additional groups from the Microsoft Graph API.

To set the proper permissions on the Azure app:

Locate the application under "App Registrations" in Azure
Navigate to the "API Permissions" page for the application
Add a permission
Select "Microsoft Graph"
Select "Delegated permissions"
Add the User.Read permission
Check the "Grant admin consent for Default Directory" checkbox

Configure the OIDC auth method in Vault by setting "provider_config" to Azure.

vault write auth/oidc/config -<<"EOH"
{
  "oidc_client_id": "your_client_id",
  "oidc_client_secret": "your_client_secret",
  "default_role": "your_default_role",
  "oidc_discovery_url": "https://login.microsoftonline.com/tenant_id/v2.0",
  "provider_config": {
     "provider": "azure"
  }
}
EOH

Add "profile" to oidc_scopes so the user's ID comes back on the JWT.

vault write auth/oidc/role/your_default_role \
 user_claim="sub" \
 allowed_redirect_uris="http://localhost:8250/oidc/callback,https://online_version_hostname:port_number/ui/vault/auth/oidc/oidc/callback"  \
 groups_claim="groups" \
 oidc_scopes="profile" \
 policies="default"