Get (retrieve) OAuth2 access token in ASP.Net Web API

Currently I am about to develop an API which needs to implement OAuth2 as a security protocol

I would like to know how to implement from scratch to generate the access token and how to refresh the token as such after a certain time

I already get the token

OAuthAuthorizationServerOptions opcionesautorizacion =
   new OAuthAuthorizationServerOptions()
   {
       AllowInsecureHttp = true,
       TokenEndpointPath = new PathString("/recuperartoken"),
       AccessTokenExpireTimeSpan = TimeSpan.FromMinutes(strTiempo),
       Provider = new Credentials.AutorizacionCredencialesToken(),
       RefreshTokenProvider = new Credentials.RefreshToken()
   };

The class as such uses this code, the variables that are assigned are obtained from a separate list, so the comparison is already made there

public override async Task GrantResourceOwnerCredentials(OAuthGrantResourceOwnerCredentialsContext context)
{
    var acceso = ((strUsuarioAdmin == context.UserName && context.Password == strPassAdmin) || (strUsuarioCliente == context.UserName && context.Password == strPassCliente));
    if (acceso == false)
    {
        context.SetError("Error de acceso", "Credenciales incorrectas"); 
    }
    else
    {
        ClaimsIdentity identidad = new ClaimsIdentity(context.Options.AuthenticationType);
        identidad.AddClaim(new Claim(ClaimTypes.Name, context.Password));
        //
        if ((strUsuarioAdmin == context.UserName && context.Password == strPassAdmin))
        {
            identidad.AddClaim(new Claim(ClaimTypes.Role, "ADMINISTRADOR"));
            context.Validated(identidad);
        }
        if ((strUsuarioCliente == context.UserName && context.Password == strPassCliente))
        {
            identidad.AddClaim(new Claim(ClaimTypes.Role, "USUARIO"));
            context.Validated(identidad);
        } 
    }
}

I would like to obtain the access_token to store it