Fetching OpenIdConnectConfiguration while offline/no connection to AuthServer - security

Question

I've been working on how to save OpenIdConnecConfiguration locally in the odd case that the AuthServer is not reachable but the frontend client (e.g. Phone) still has a valid refresh token which still needs to be validated again when signing in. It is also needed to be saved locally to a file in the case that the backend (e.g. WCF) has restarted due to a update or the frequent restarts it has (once a day)
What I've done so far, I've saved the JSON object of the ".well-known/openid-configuration" to a file/variable and now I want to create the OpenIdConnectConfiguration object.
OpenIdConnectConfiguration.Create(json) does a lot of the work but the signingKeys do not get created. I think maybe it's because the authorization endpoint needs to be created in some other manner maybe?
Or maybe I'm doing this the wrong way and there is another solution to this issue. I'm working in C#.
Edit: I know there are some caveats to what I'm doing. I need to check once in awhile to see if the public key has been changed, but security wise it should be fine to save the configuration because it's already public. I only need the public key to validate/sign the jwt I get from the user and nothing more.

Answer 1

Figured out a solution after looking through OpenIdConnectConfiguration.cs on the official github.
When fetching the OpenIdConnectConfiguration the first time, use Write() to get a JSON string and use it to save it to file.
Afterwards when loading the file, use Create() to create the OpenIdConnectConfiguration again from the JSON string (This had the issue of not saving the signingKeys as said in the question, but alas! there is a fix)
Lastly to fix the issue with the signingKeys not being created, (this is what I found out from the github class) all we need to do is loop through the JsonWebKeySet and create them as is done in the class. We already have all the information needed from the initial load and therefore only need to create them again.
I'll leave the code example below of what I did. I still need to handle checking if he key has been changed/expired which is the next step I'll be tackling.
interface IValidationPersistence
{
void SaveOpenIdConnectConfiguration(OpenIdConnectConfiguration openIdConfig);
OpenIdConnectConfiguration LoadOpenIdConnectionConfiguration();
}
class ValidationPersistence : IValidationPersistence
{
private readonly string _windowsTempPath = Path.GetTempPath();
private readonly string _fileName = "TestFileName";
private readonly string _fullFilePath;
public ValidationPersistence()
{
_fullFilePath = _windowsTempPath + _fileName;
}
public OpenIdConnectConfiguration LoadOpenIdConnectionConfiguration()
{
FileService fileService = new FileService();
OpenIdConnectConfiguration openIdConfig = OpenIdConnectConfiguration.Create(fileService.LoadFromJSONFile<string>(_fullFilePath));
foreach (SecurityKey key in openIdConfig.JsonWebKeySet.GetSigningKeys())
{
openIdConfig.SigningKeys.Add(key);
}
return openIdConfig;
}
public void SaveOpenIdConnectConfiguration(OpenIdConnectConfiguration openIdConfig)
{
FileService fileService = new FileService();
fileService.WriteToJSONFile(OpenIdConnectConfiguration.Write(openIdConfig), _fullFilePath);
}
}