Configure.cs

var tokenValidationParameters = new TokenValidationParameters()
{
    RequireExpirationTime = true,
    ValidateIssuer = false,
    ValidateAudience = false,
    IssuerSigningKey = new SymmetricSecurityKey(Convert.FromBase64String(SecretKey))
};
app.UseJwtBearerAuthentication(new JwtBearerOptions
{
    AutomaticAuthenticate = true,
    AutomaticChallenge = true,
    TokenValidationParameters = tokenValidationParameters
});