Utilize refresh token and exchange for access token at startup

Program.cs

@@ -2,6 +2,10 @@
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Hosting;
 using Microsoft.Extensions.Logging;
+using System.Net.Http.Json;
+
+const string GoogleApiKey = "AIzaSyDFYtBIYm-Z9HUbMTcB-4vP1FJMm7lX4LA";
+var httpClient = new HttpClient();
 
 var hostBuilder = Host.CreateApplicationBuilder(args);
 hostBuilder.Configuration.AddUserSecrets<Program>();
@@ -11,16 +15,13 @@
 
 var logger = scope.ServiceProvider.GetRequiredService<ILogger<Program>>();
 
-if (args.Length == 0)
-{
-    logger.LogError("No operations specified.");
+var token = await RetrieveTokenAsync();
+if (token == null)
     return -1;
-}
 
-var token = hostBuilder.Configuration["AuthorizationToken"];
-if (string.IsNullOrEmpty(token) || token == "SECRET")
+if (args.Length == 0)
 {
-    logger.LogError("No authorization token secret provided.");
+    logger.LogError("No operations specified.");
     return -1;
 }
 
@@ -43,6 +44,41 @@
 
 return 0;
 
+async Task<string?> RetrieveTokenAsync()
+{
+    var refreshToken = hostBuilder.Configuration["RefreshToken"];
+    if (string.IsNullOrEmpty(refreshToken) || refreshToken == "SECRET")
+    {
+        logger.LogError("No refresh token secret provided.");
+        return null;
+    }
+
+    try
+    {
+        using HttpResponseMessage response = await httpClient.PostAsync(
+            $"https://securetoken.googleapis.com/v1/token?key={GoogleApiKey}",
+            new FormUrlEncodedContent(new Dictionary<string, string>
+            {
+                ["grant_type"] = "refresh_token",
+                ["refresh_token"] = refreshToken
+            }));
+        response.EnsureSuccessStatusCode();
+
+        var tokenResponse = await response.Content.ReadFromJsonAsync<Dictionary<string, string>>();
+        if (tokenResponse == null || tokenResponse["access_token"] == null)
+        {
+            return null;
+        }
+
+        return tokenResponse["access_token"];
+    }
+    catch (Exception ex)
+    {
+        logger.LogError(ex, "Failed to authorize.");
+        return null;
+    }
+}
+
 void UpdateCollectionPrices()
 {
     // TODO

appsettings.json

@@ -1,3 +1,3 @@
 {
-    "AuthorizationToken": "SECRET"
+    "RefreshToken": "SECRET"
 }

invintory-updater.csproj

@@ -18,6 +18,7 @@
   <ItemGroup>
     <PackageReference Include="Microsoft.Extensions.Configuration.UserSecrets" Version="8.0.0" />
     <PackageReference Include="Microsoft.Extensions.Hosting" Version="8.0.0" />
+    <PackageReference Include="System.Net.Http.Json" Version="8.0.0" />
   </ItemGroup>
 
 </Project>