Function check_cross_signing_key 

fn check_cross_signing_key(
    expected_user_id: &UserId,
    expected_usage: &KeyUsage,
    user_devices: &[Device],
    key: &CrossSigningKey,
) -> Result<(), CrossSigningKeysError>

Performs various checks on a [CrossSigningKey].

Errors

This function returns a InputJsonError error for any of the following cases:

• The key is malformed in some way (e.g missing a field, does not have exactly one entry in its keys field, etc).
• The cross-signing key’s id is the same as one of the user’s device_ids (See https://spec.matrix.org/v1.16/client-server-api/#key-and-signature-security).
• The user ID of the key does not match that of the authenticated user making the request.