Creates a new custom OIDC/OAuth provider. For OIDC providers, the server fetches and validates the discovery document at creation time and throws an AuthException with code validation_failed if it is unreachable or invalid.
The provider configuration, including `providerType`, `identifier`, `name`, `clientId`, `clientSecret`, and optional fields such as `customClaimsAllowlist`.
final CustomOAuthProvider provider =
await supabase.auth.admin.customProviders.createProvider(
CreateCustomProviderParams(
providerType: CustomProviderType.oidc,
identifier: 'custom:mycompany',
name: 'My Company',
clientId: 'client-id',
clientSecret: 'client-secret',
issuer: 'https://auth.mycompany.com',
customClaimsAllowlist: ['groups', 'org_id'],
),
);