Microsoft.IdentityModel (JsonWebTokenHandler)

Facts and the checks behind them

Nothing below is copied from documentation. The check content/libraries/verify/microsoft-identitymodel/run.sh ran Microsoft.IdentityModel (JsonWebTokenHandler) 8.23.0 in the container image mcr.microsoft.com/dotnet/sdk:10.0.402-noble on October 20, 2026; the page must match what it printed, and each fact lists those lines.

• JWS algorithms

  HS256HS384HS512RS256RS384RS512PS256PS384PS512ES256ES384ES512

  HS, RS, PS and ES at 256/384/512 signed and validated; no EdDSA key type exists in the package.

  Recorded by the check

  fact jws-algorithms = HS256, HS384, HS512, RS256, RS384, RS512, PS256, PS384, PS512, ES256, ES384, ES512
  evidence jws-algorithms: EdDSA signing with an ECDsaSecurityKey or other built-in key: no EdDSA security key type

• ES256 signature encoding

  raw

  ES256 signatures are 64 bytes of raw r‖s.

  Recorded by the check

  fact jws-ecdsa-encoding = raw

• DER signature inside a JWS

  rejected

  A DER-encoded ES256 signature fails with IDX10517: Signature validation failed.

  Recorded by the check

  fact jws-der-signature = rejected
  evidence jws-der-signature: SecurityTokenSignatureKeyNotFoundException: IDX10517: Signature validation failed. The token's kid is missing. Keys tried:

• Algorithm allow-list

  from-key

  With ValidAlgorithms null, the key decides: an RS256 token against an EC key failed with IDX10517.

  Recorded by the check

  fact jwt-algorithm-allowlist = from-key
  evidence jwt-algorithm-allowlist: ValidAlgorithms null, RS256 token against the EC key: SecurityTokenSignatureKeyNotFoundException: IDX10517: Signature validation failed. The token's kid is missing. Keys tried:

• Unsigned tokens (alg none)

  opt-in

  Unsigned tokens fail with IDX10504: Unable to validate signature, token does not have a signature by default and validate with RequireSignedTokens = false.

  Recorded by the check

  fact jwt-alg-none = opt-in
  evidence jwt-alg-none: default parameters: SecurityTokenInvalidSignatureException: IDX10504: Unable to validate signature, token does not have a signature:
  evidence jwt-alg-none: RequireSignedTokens = false: valid

• Public key used as an HMAC secret

  rejected

  An HS256 token keyed with the PEM text failed against the EC key with IDX10517.

  Recorded by the check

  fact jwt-hmac-public-key = rejected
  evidence jwt-hmac-public-key: HS256 token keyed with the PEM text, EC key, ValidAlgorithms null: SecurityTokenSignatureKeyNotFoundException: IDX10517: Signature validation failed. The token's kid is missing. Keys tried:

• Curve checked against alg

  not-enforced

  CreateToken signed ES256 with a P-384 key, and validation with that key and ValidAlgorithms set to ES256 succeeded.

  Recorded by the check

  fact jwt-ecdsa-curve-check = not-enforced
  evidence jwt-ecdsa-curve-check: ES256 with a P-384 key: signed; validation: valid

• Default clock skew

  300s

  TokenValidationParameters.DefaultClockSkew is 5 minutes: tokens expired up to about 300 seconds earlier still validated.

  Recorded by the check

  fact jwt-clock-skew = 300s
  evidence jwt-clock-skew: TokenValidationParameters.DefaultClockSkew = 00:05:00

• Expiry claim required

  yes

  A token without exp fails with SecurityTokenNoExpirationException: IDX10225.

  Recorded by the check

  fact jwt-exp-required = yes
  evidence jwt-exp-required: CreateToken without Expires adds exp anyway: True
  evidence jwt-exp-required: hand-built HS256 token without exp: SecurityTokenNoExpirationException: IDX10225: Lifetime validation failed. The token is missing an Expiration Time. Tokentype:

• Error details hidden by default

  yes

  Validation errors replace token contents with [PII of type ... is hidden]; setting IdentityModelEventSource.ShowPII = true removed the placeholder.

  Recorded by the check

  fact error-detail-hidden-by-default = yes
  evidence error-detail-hidden-by-default: PII placeholder in the default message: True; after IdentityModelEventSource.ShowPII = true: False

Usage

using System.Security.Cryptography;
using Microsoft.IdentityModel.JsonWebTokens;
using Microsoft.IdentityModel.Tokens;

var key = new ECDsaSecurityKey(ECDsa.Create(ECCurve.NamedCurves.nistP256)) { KeyId = "2026-10" };
var handler = new JsonWebTokenHandler();
var token = handler.CreateToken(new SecurityTokenDescriptor
{
    Issuer = "https://auth.example.com",
    Audience = "api",
    Claims = new Dictionary<string, object> { ["sub"] = "user-42" },
    Expires = DateTime.UtcNow.AddMinutes(10),
    SigningCredentials = new SigningCredentials(key, SecurityAlgorithms.EcdsaSha256),
});

// Pin the algorithm (ES256 is not tied to P-256 here) and shrink the 5-minute default skew.
var result = await handler.ValidateTokenAsync(token, new TokenValidationParameters
{
    IssuerSigningKey = key,
    ValidIssuer = "https://auth.example.com",
    ValidAudience = "api",
    ValidAlgorithms = new[] { SecurityAlgorithms.EcdsaSha256 },
    ClockSkew = TimeSpan.FromSeconds(30),
});
Console.WriteLine($"valid: {result.IsValid}, sub: {result.Claims["sub"]}");