Empty claims with OIDC provider on Authentik

Nobody has claimed this yet.

I try to implement Goth with generic OIDC providers like Authentik. The configurations for GitHub, AzureAD and Keycloak are working totally finbe, but with Authentik and the configuration below results in empty claims as I don't get a nickname, email or name of the authenticated user.

Has somebody else faced this issue and got an idea how to resolve that? If there is some information missing I try my best to deliver the missing parts.

```
provider, err := openidConnect.NewNamed(
"authentik",
"REDACTED",
"REDACTED",
"http://localhost:8080/api/v1/auth/authentik-oidc/callback",
"https://authentik.example.com/application/o/example/.well-known/openid-configuration",
[]string{},
)

if err != nil {
return nil, err
}

provider.NickNameClaims = []string{
"preferred_username",
}

provider.NameClaims = []string{
"name",
}

provider.EmailClaims = []string{
"email",
}
```

Start with the openidConnect.NewNamed configuration shown in the issue and reproduce the Authentik flow using the provided discovery URL and callback. Compare the resulting claims with the working GitHub, AzureAD, and Keycloak configurations, focusing on why nickname, email, and name remain empty. Done means the Authentik login produces the expected user claims or the missing provider requirements are documented.

Written by the indexing model from the issue text.