find nameId of specific user with a given loginid in org

The query [1] will list all users with samlIds in the org, but how can I craft the query to search for a user with a specific `login`?

[1]
```
query Users($org: String!, $first: Int = 100, $after: String) {
organization(login: $org) {
samlIdentityProvider {
externalIdentities(first: $first, after: $after) {
edges {
node {
guid,
samlIdentity {
nameId
}
user {
login
}
}
}
pageInfo {
hasNextPage
endCursor
}
}
}
}
}
```

Start with the Users GraphQL query included in the issue and inspect the relevant organization external-identities fields. Determine whether the query can target a specific login and document the resulting query or limitation, including how it returns that user's nameId.

Written by the indexing model from the issue text.