fix(generic): check local token expiry

src/shared/Core/Authentication/OAuth/Json/WebToken.cs

@@ -0,0 +1,60 @@
+using System;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace GitCredentialManager.Authentication.Oauth.Json
+{
+    public class WebToken(WebToken.TokenHeader header, WebToken.TokenPayload payload, string signature)
+    {
+        public class TokenHeader
+        {
+            [JsonRequired]
+            [JsonInclude]
+            [JsonPropertyName("typ")]
+            public string Type { get; private set; }
+        }
+        public class TokenPayload
+        {
+            [JsonRequired]
+            [JsonInclude]
+            [JsonPropertyName("exp")]
+            public long Expiry { get; private set; }
+        }
+        public TokenHeader Header { get; } = header;
+        public TokenPayload Payload { get; } = payload;
+        public string Signature { get; } = signature;
+
+        public bool IsExpired
+        {
+            get
+            {
+                return Payload.Expiry < DateTimeOffset.Now.ToUnixTimeSeconds();
+            }
+        }
+
+        static public bool TryCreate(string value, out WebToken jwt)
+        {
+            jwt = null;
+            try
+            {
+                var parts = value.Split('.');
+                if (parts.Length != 3)
+                {
+                    return false;
+                }
+                var header = JsonSerializer.Deserialize<TokenHeader>(Base64UrlConvert.Decode(parts[0]));
+                if (!"JWT".Equals(header.Type))
+                {
+                    return false;
+                }
+                var payload = JsonSerializer.Deserialize<TokenPayload>(Base64UrlConvert.Decode(parts[1]));
+                jwt = new WebToken(header, payload, parts[2]);
+                return true;
+            }
+            catch
+            {
+                return false;
+            }
+        }
+    }
+}

src/shared/Core/Base64UrlConvert.cs

@@ -4,22 +4,43 @@ namespace GitCredentialManager
 {
     public static class Base64UrlConvert
     {
+
+        // The base64url format is the same as regular base64 format except:
+        //   1. character 62 is "-" (minus) not "+" (plus)
+        //   2. character 63 is "_" (underscore) not "/" (slash)
+        //   3. padding is optional
+        private const char base64PadCharacter = '=';
+        private const char base64Character62 = '+';
+        private const char base64Character63 = '/';
+        private const char base64UrlCharacter62 = '-';
+        private const char base64UrlCharacter63 = '_';
+
         public static string Encode(byte[] data, bool includePadding = true)
         {
-            const char base64PadCharacter = '=';
-            const char base64Character62 = '+';
-            const char base64Character63 = '/';
-            const char base64UrlCharacter62 = '-';
-            const char base64UrlCharacter63 = '_';
-
-            // The base64url format is the same as regular base64 format except:
-            //   1. character 62 is "-" (minus) not "+" (plus)
-            //   2. character 63 is "_" (underscore) not "/" (slash)
             string base64Url = Convert.ToBase64String(data)
                 .Replace(base64Character62, base64UrlCharacter62)
                 .Replace(base64Character63, base64UrlCharacter63);
 
             return includePadding ? base64Url : base64Url.TrimEnd(base64PadCharacter);
         }
+
+        public static byte[] Decode(string data)
+        {
+            string base64 = data
+                .Replace(base64UrlCharacter62, base64Character62)
+                .Replace(base64UrlCharacter63, base64Character63);
+
+            switch (base64.Length % 4)
+            {
+                case 2:
+                    base64 += base64PadCharacter;
+                    goto case 3;
+                case 3:
+                    base64 += base64PadCharacter;
+                    break;
+            }
+
+            return Convert.FromBase64String(base64);
+        }
     }
 }

src/shared/Core/GenericHostProvider.cs

@@ -5,6 +5,7 @@
 using System.Threading;
 using System.Threading.Tasks;
 using GitCredentialManager.Authentication;
+using GitCredentialManager.Authentication.Oauth.Json;
 using GitCredentialManager.Authentication.OAuth;
 
 namespace GitCredentialManager
@@ -125,6 +126,20 @@ public override async Task<ICredential> GenerateCredentialAsync(InputArguments i
             return await _basicAuth.GetCredentialsAsync(uri.AbsoluteUri, input.UserName);
         }
 
+        public override async Task<ICredential> GetCredentialAsync(InputArguments input)
+        {
+            var credential = await base.GetCredentialAsync(input);
+            // discard credential if it's an already expired JSON Web Token
+            if (WebToken.TryCreate(credential.Password, out var token) && token.IsExpired)
+            {
+                // No existing credential was found, create a new one
+                Context.Trace.WriteLine("Refreshing expired JWT credential...");
+                credential = await GenerateCredentialAsync(input);
+                Context.Trace.WriteLine("Credential created.");
+            }
+            return credential;
+        }
+
         private async Task<ICredential> GetOAuthAccessToken(Uri remoteUri, string userName, GenericOAuthConfig config, ITrace2 trace2)
         {
             // TODO: Determined user info from a webcall? ID token? Need OIDC support
@@ -150,9 +165,9 @@ private async Task<ICredential> GetOAuthAccessToken(Uri remoteUri, string userNa
             string refreshService = new UriBuilder(remoteUri) { Host = $"refresh_token.{remoteUri.Host}" }
                 .Uri.AbsoluteUri.TrimEnd('/');
 
-            // Try to use a refresh token if we have one
+            // Try to use a refresh token if we have one (unless it's an expired JSON Web Token)
             ICredential refreshToken = Context.CredentialStore.Get(refreshService, userName);
-            if (refreshToken != null)
+            if (refreshToken != null && !(WebToken.TryCreate(refreshToken.Password, out var token) && token.IsExpired))
             {
                 try
                 {