RefreshTokenAsync.cs

public async Task<AuthenticationResult> RefreshTokenAsync(string token, string refreshToken)
{
    var validatedToken = GetPrincipalFromToken(token);

    if (validatedToken == null)
    {
        return new AuthenticationResult {Errors = new[] {"Invalid Token"}};
    }

    var expiryDateUnix =
        long.Parse(validatedToken.Claims.Single(x => x.Type == JwtRegisteredClaimNames.Exp).Value);

    var expiryDateTimeUtc = new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc)
        .AddSeconds(expiryDateUnix);

    if (expiryDateTimeUtc > DateTime.UtcNow)
    {
        return new AuthenticationResult {Errors = new[] {"This token hasn't expired yet"}};
    }

    var jti = validatedToken.Claims.Single(x => x.Type == JwtRegisteredClaimNames.Jti).Value;

    var storedRefreshToken = await _context.RefreshTokens.SingleOrDefaultAsync(x => x.Token == refreshToken);

    if (storedRefreshToken == null)
    {
        return new AuthenticationResult {Errors = new[] {"This refresh token does not exist"}};
    }

    if (DateTime.UtcNow > storedRefreshToken.ExpiryDate)
    {
        return new AuthenticationResult {Errors = new[] {"This refresh token has expired"}};
    }

    if (storedRefreshToken.Invalidated)
    {
        return new AuthenticationResult {Errors = new[] {"This refresh token has been invalidated"}};
    }

    if (storedRefreshToken.Used)
    {
        return new AuthenticationResult {Errors = new[] {"This refresh token has been used"}};
    }

    if (storedRefreshToken.JwtId != jti)
    {
        return new AuthenticationResult {Errors = new[] {"This refresh token does not match this JWT"}};
    }

    storedRefreshToken.Used = true;
    _context.RefreshTokens.Update(storedRefreshToken);
    await _context.SaveChangesAsync();

    var user = await _userManager.FindByIdAsync(validatedToken.Claims.Single(x => x.Type == "id").Value);
    return await GenerateAuthenticationResultForUserAsync(user);
}