I need to create JWT using RS512 and private key which is string value.
I tried the following way:

```
        var privateKey = @"-----BEGIN PRIVATE KEY----- {some string data} -----END PRIVATE KEY-----";

        var securityKey = new SymmetricSecurityKey(Encoding.UTF8.GetBytes(privateKey));
        var credentials = new SigningCredentials(securityKey, SecurityAlgorithms.RsaSha512);
        var header = new JwtHeader(credentials);

        var now = DateTime.UtcNow;
        var payload = new JwtPayload
        {
            { "iss", "1198bef0-a0d52731-706e-4936-be46-1ae4b2b2e9bd" },
            { "iat", now },
            { "exp", now.AddMinutes(30) }
        };

        var secToken = new JwtSecurityToken(header, payload);
        var handler = new JwtSecurityTokenHandler();

        var tokenString = handler.WriteToken(secToken);

```

But it gets me the next error:

```
        NotSupportedException: IDX10634: Unable to create the SignatureProvider.
Algorithm: 'RS512', SecurityKey: 'Microsoft.IdentityModel.Tokens.SymmetricSecurityKey, KeyId: '', InternalId: '546ecdc1-0c87-40b4-905e-88d3bfc032c3'.'
is not supported. The list of supported algorithms is available here: https://aka.ms/IdentityModel/supported-algorithms

```

I heard that I should use `RsaSecurityKey` instead of `SymmetricSecurityKey` for RS512, but I couldn't find how to use one with private key.

Thanks!