WCF WindowsIdentity Impersonation Service - Unable to load DLL 'security.Dll'

I'm trying to create a WCF service for SAML impersonation. The idea is that the WCF Service uses the WindowsIdentity (Service for User Logon) and Identity Delegation features to create a Delegation SAML Token via ADFS that can be used to authenticate as this user in another service based on IdP-initiated SAML login flow.

This is my first time working with .NET, C# and ASP-Web Apps, so there may be issues within the Code or configuration (ADFS, IIS, certificates etc.)

So far my idea (important code pieces) is as follows:

    private static GenericXmlSecurityToken GetServiceTokenForUser(string usernameAtDomain)
    {
        // Obtain the user Identity token using WindowsIdentityConstructor
        WindowsIdentity winId = new WindowsIdentity(usernameAtDomain);
        WindowsImpersonationContext ctx = winId.Impersonate();

        GenericXmlSecurityToken token = null;
        try
        {
            // via impersonated user, 
            token = GetServiceTokenForUser();
        } finally
        {
            ctx.Undo();
        }
        return token;
    }

    [OperationBehavior(Impersonation = ImpersonationOption.Allowed)]
    private static GenericXmlSecurityToken GetServiceTokenForUser()
    { 
        EndpointAddress endpoint;
        GenericXmlSecurityToken securityToken;
        RequestSecurityToken rst;
        RequestSecurityTokenResponse rstr;
        WindowsWSTrustBinding binding;
        WSTrustChannel channel;
        WSTrustChannelFactory factory;

        //ignores certificates error
        ServicePointManager.ServerCertificateValidationCallback = (x, y, z, w) => true;

        // use WindowsWSTrustBinding for credentials -> should be the impersonated user
        binding = new WindowsWSTrustBinding(SecurityMode.TransportWithMessageCredential);

        endpoint = new EndpointAddress(new Uri(stsEndpoint));
        factory = new WSTrustChannelFactory(binding, endpoint);
        factory.TrustVersion = TrustVersion.WSTrust13;

        rst = new RequestSecurityToken 
        {
            AppliesTo = new EndpointReference(relyingPartyId),
            KeyType = KeyTypes.Bearer,
            RequestType = RequestTypes.Issue,
            TokenType = "http://docs.oasis-open.org/wss/oasis-wss-saml-token-profile-1.1#SAMLV2.0"
        };

        channel = (WSTrustChannel)factory.CreateChannel();
        // retrieve valid SAML security token
        SecurityToken issuedToken = channel.Issue(rst, out rstr);
        securityToken = issuedToken as GenericXmlSecurityToken;
        return securityToken;
    }

When trying to run that in an endpoint that should just return the generated SAML Token (for now), I'm currently running into the following issue:

Unable to load DLL 'security.Dll': Either a required impersonation level was not provided, or the provided impersonation level is invalid. (Exception from HRESULT: 0x80070542)
Server stack trace: 
   at System.IdentityModel.SafeFreeCredentials.AcquireCredentialsHandle(String package, CredentialUse intent, AuthIdentityEx& authdata, SafeFreeCredentials& outCredential)
   at System.IdentityModel.SspiWrapper.AcquireCredentialsHandle(String package, CredentialUse intent, AuthIdentityEx& authdata)
   at System.ServiceModel.Security.SecurityUtils.GetCredentialsHandle(String package, NetworkCredential credential, Boolean isServer, String[] additionalPackages)

I arrived at this error after adding various necessary packages to the project, e.g. Microsoft.IdentityModel.

From my understanding, the service is unable to access the security.dll. However, the system's security.dll exists in C:\Windows\System32.

The Error Either a required impersonation level was not provided, or the provided impersonation level is invalid suggests that there might be something wrong with the impersonation grant. I found various articles that solve similar issues by adding certain configuration to either the server's Web.config, or the client's App.config, but trying to adjust them didn't work in my case (it's very possible however that I didn't adjust the configuration file properly).

Any help with this topic is highly appreciated! Please let me know if you are missing any information in this Question that I should provide additionally.