set clock skew to 0 (Issue/1964-tokenExpiryUIv2)

src/JwtHandler/JwtHandler.cs

@@ -15,8 +15,10 @@ namespace Coscine.JwtHandler
         private readonly JwtSecurityTokenHandler _jwtSecurityTokenHandler;
         private readonly SymmetricSecurityKey _symmetricSecurityKey;
         private readonly DateTime _centuryBegin;
+
         // How long the default token is valid (in minutes).
         private readonly double _defaultExpiration;
+
         private readonly string _issuer;
         private readonly string _audience;
 
@@ -52,7 +54,9 @@ namespace Coscine.JwtHandler
                 ValidateIssuerSigningKey = true,
                 IssuerSigningKey = _symmetricSecurityKey,
                 ValidateIssuer = false,
-                ValidateAudience = false
+                ValidateAudience = false,
+                // set clockskew to zero so tokens expire exactly at token expiration time (instead of 5 minutes later)
+                ClockSkew = TimeSpan.Zero
             };
 
             _jwtSecurityTokenHandler.ValidateToken(token, tokenValidationParameters, out _);
@@ -107,6 +111,5 @@ namespace Coscine.JwtHandler
 
             return GenerateJwtToken(payload, issuer, audience, issuedAt, expires, signatureAlgorithm);
         }
-
     }
 }
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