Calling Snap to Roads Google API from C#. This code has mainly been created using Xamarin Libraries, so It might not work on other platforms.

GoogleRoads.cs

using Xamarin.Forms.Maps;
using System;
using System.Collections.Generic;
using System.Linq;
using Newtonsoft.Json;
using System.Threading.Tasks;

public static class GoogleRoads
{
    /// <summary>
    /// Using Google API, snaps a list of given points to a list of points snapped to the roads.
    /// </summary>
    /// <param name="pPoints"></param>
    /// <param name="pGoogleApiKey"></param>
    /// <returns></returns>
    public static async Task<IEnumerable<Position>> SnapToRoads(IEnumerable<Position> pPoints, string pGoogleApiKey, bool pInterpolate)
    {
        string points = String.Empty;

        try
        {
            // Generate an array of strings with latitude and longituded, separeted by comma
            string[] strPoints = pPoints.Select(pnts => $"{pnts.Latitude},{pnts.Longitude}").ToArray();

            // Join the strings together using a pipe character.
            string parameter = $"path={string.Join("|", strPoints)}";

            // Generate the URL
            Uri url = new Uri($"https://roads.googleapis.com/v1/snapToRoads?{parameter}&key={pGoogleApiKey}&interpolate={pInterpolate}");

            // Make the request and get the json String.
            points = await ServiceManager.GetStringAsync(url);

            // Get the response
            SnappedPointsRoot pointsResponse = JsonConvert.DeserializeObject<SnappedPointsRoot>(points);

            // Convert the points to a list of position.
            IEnumerable<Position> retVal = pointsResponse.SnappedPoints.Select(sp => new Position(sp.Location.Latitude, sp.Location.Longitude));

            // Return the values.
            return retVal;
        }
        catch (Exception ex)
        {
            throw new Exception("An unhandled exception occurred while snapping points to roads using Google API.", ex);
        }
    }
}

ServiceManager.cs

using System;
using System.Net.Http;
using System.Threading.Tasks;

public static class ServiceManager
{
    /// <summary>
    /// Returns a string using the GET verb.
    /// </summary>
    /// <param name="url">The URL to make the request from.</param>
    /// <returns></returns>
    public static async Task<string> GetStringAsync(Uri url)
    {
        try
        {
            // Instantiate the HttpClient
            HttpClient client = new HttpClient();
            
            // Make the GET request.
            HttpResponseMessage response = await client.GetAsync(url);
            
            try
            {
                // Make sure the status code is Success
                response.EnsureSuccessStatusCode();
            }
            catch (HttpRequestException ex)
            {
                // Get the error string
                string error = await response.Content.ReadAsStringAsync();
                return error;

            }

            // Get the string response.
            string retVal = await response.Content.ReadAsStringAsync();
            
            // Return the response string.
            return retVal;
        }
        catch (Exception ex)
        {
            throw ex;
        }
    }
}

SnappedPoint.cs

using Newtonsoft.Json;
using System;
using System.Collections.Generic;
using System.Text;

public class SnappedPoint
{
    /// <summary>
    /// The location of the snapped point.
    /// </summary>
    [JsonProperty("location")]
    public Location Location { get; set; }

    /// <summary>
    /// An integer value indicating the corresponding value on the original request. Each value on the request must lead to a value adjusted to the response.
    /// </summary>
    [JsonProperty("originalIndex")]
    public int OriginalIndex { get; set; }

    /// <summary>
    /// A unique identifier for a site.
    /// </summary>
    [JsonProperty("placeId")]
    public string PlaceId { get; set; }
}

SnappedPointsRoot.cs

using Newtonsoft.Json;
using System;
using System.Collections.Generic;
using System.Text;

public class SnappedPointsRoot
{
    /// <summary>
    /// A list of snapped points.
    /// </summary>
    [JsonProperty("snappedPoints")]
    public SnappedPoint[] SnappedPoints { get; set; }
}