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Merged
josephdecock merged 1 commit into from
Jan 28, 2025
Merged

Add option for strict validation of assertion audiences #1737

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5 changes: 5 additions & 0 deletions ...ver/src/IdentityServer/Configuration/DependencyInjection/Options/IdentityServerOptions.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -69,6 +69,11 @@ public class IdentityServerOptions
/// </summary>
public bool StrictJarValidation { get; set; } = false;

/// <summary>
/// When clients authenticate with private_key_jwt assertions, validate the audience of the assertion strictly: the audience must be this IdentityServer's issuer identifier as a single string.
/// </summary>
public bool StrictClientAssertionAudienceValidation { get; set; } = false;

/// <summary>
/// Specifies if a user's tenant claim is compared to the tenant acr_values parameter value to determine if the login page is displayed. Defaults to false.
/// </summary>
Expand Down
100 changes: 82 additions & 18 deletions identity-server/src/IdentityServer/Validation/Default/PrivateKeyJwtSecretValidator.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -89,20 +89,7 @@ public async Task<SecretValidationResult> ValidateAsync(IEnumerable<Secret> secr
return fail;
}

var validAudiences = new[]
{
// token endpoint URL
string.Concat(_urls.BaseUrl.EnsureTrailingSlash(), ProtocolRoutePaths.Token),
// issuer URL + token (legacy support)
string.Concat((await _issuerNameService.GetCurrentAsync()).EnsureTrailingSlash(), ProtocolRoutePaths.Token),
// issuer URL
await _issuerNameService.GetCurrentAsync(),
// CIBA endpoint: https://openid.net/specs/openid-client-initiated-backchannel-authentication-core-1_0.html#auth_request
string.Concat(_urls.BaseUrl.EnsureTrailingSlash(), ProtocolRoutePaths.BackchannelAuthentication),
// PAR endpoint: https://datatracker.ietf.org/doc/html/rfc9126#name-request
string.Concat(_urls.BaseUrl.EnsureTrailingSlash(), ProtocolRoutePaths.PushedAuthorization),

}.Distinct();
var issuer = await _issuerNameService.GetCurrentAsync();

var tokenValidationParameters = new TokenValidationParameters
{
Expand All @@ -111,15 +98,46 @@ await _issuerNameService.GetCurrentAsync(),

ValidIssuer = parsedSecret.Id,
ValidateIssuer = true,

ValidAudiences = validAudiences,
ValidateAudience = true,


RequireSignedTokens = true,
RequireExpirationTime = true,

ClockSkew = TimeSpan.FromMinutes(5)
};

if (_options.StrictClientAssertionAudienceValidation)
{
// New strict audience validation requires that the audience be the issuer identifier, disallows multiple
// audiences in an array, and even disallows wrapping even a single audience in an array
tokenValidationParameters.AudienceValidator = (audiences, token, parameters) =>
{
// There isn't a particularly nice way to distinguish between a claim that is a single string wrapped in
// an array and just a single string when using a JsonWebToken. The jwt.GetClaim function and jwt.Claims
// collection both convert that into a string valued claim. However, GetPayloadValue<object> does not do
// any type inferencing, so we can call that, and then check if the result is actually a string
var audValue = ((JsonWebToken)token).GetPayloadValue<object>("aud");
return audValue is string audString &&
AudiencesMatch(audString, issuer);
};
}
else
{
tokenValidationParameters.ValidateAudience = true;
tokenValidationParameters.ValidAudiences = new[]
{
// token endpoint URL
string.Concat(_urls.BaseUrl.EnsureTrailingSlash(), ProtocolRoutePaths.Token),
// issuer URL + token (legacy support)
string.Concat((await _issuerNameService.GetCurrentAsync()).EnsureTrailingSlash(), ProtocolRoutePaths.Token),
// issuer URL
issuer,
// CIBA endpoint: https://openid.net/specs/openid-client-initiated-backchannel-authentication-core-1_0.html#auth_request
string.Concat(_urls.BaseUrl.EnsureTrailingSlash(), ProtocolRoutePaths.BackchannelAuthentication),
// PAR endpoint: https://datatracker.ietf.org/doc/html/rfc9126#name-request
string.Concat(_urls.BaseUrl.EnsureTrailingSlash(), ProtocolRoutePaths.PushedAuthorization),

}.Distinct();
}

var handler = new JsonWebTokenHandler() { MaximumTokenSizeInBytes = _options.InputLengthRestrictions.Jwt };
var result = await handler.ValidateTokenAsync(jwtTokenString, tokenValidationParameters);
Expand Down Expand Up @@ -162,4 +180,50 @@ await _issuerNameService.GetCurrentAsync(),

return success;
}

// AudiencesMatch and AudiencesMatchIgnoringTrailingSlash are based on code from
// https://github.com/AzureAD/azure-activedirectory-identitymodel-extensions-for-dotnet/blob/bef98ca10ae55603ce6d37dfb7cd5af27791527c/src/Microsoft.IdentityModel.Tokens/Validators.cs#L158-L193
private bool AudiencesMatch(string tokenAudience, string validAudience)
{
if (validAudience.Length == tokenAudience.Length)
{
if (string.Equals(validAudience, tokenAudience))
{
return true;
}
}

return AudiencesMatchIgnoringTrailingSlash(tokenAudience, validAudience);
}

private bool AudiencesMatchIgnoringTrailingSlash(string tokenAudience, string validAudience)
{
int length = -1;

if (validAudience.Length == tokenAudience.Length + 1 &&
validAudience.EndsWith("/", StringComparison.InvariantCulture))
{
length = validAudience.Length - 1;
}
else if (tokenAudience.Length == validAudience.Length + 1 &&
tokenAudience.EndsWith("/", StringComparison.InvariantCulture))
{
length = tokenAudience.Length - 1;
}

// the length of the audiences is different by more than 1 and neither ends in a "/"
if (length == -1)
{
return false;
}

if (string.CompareOrdinal(validAudience, 0, tokenAudience, 0, length) == 0)
{
_logger.LogInformation("Audience Validated.Audience: '{audience}'", tokenAudience);

return true;
}

return false;
}
}
120 changes: 104 additions & 16 deletions ...-server/test/IdentityServer.UnitTests/Validation/Secrets/PrivateKeyJwtSecretValidation.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,7 @@
using System.Collections.Generic;
using System.IdentityModel.Tokens.Jwt;
using System.Security.Claims;
using System.Text.Json;
using System.Threading.Tasks;
using Duende.IdentityServer;
using Duende.IdentityServer.Configuration;
Expand All @@ -28,32 +29,47 @@ public class PrivateKeyJwtSecretValidation
{
private readonly ISecretValidator _validator;
private readonly IClientStore _clients;
private readonly IdentityServerOptions _options;

public PrivateKeyJwtSecretValidation()
{
_options = new IdentityServerOptions();

_validator = new PrivateKeyJwtSecretValidator(
new TestIssuerNameService("https://idsrv3.com"),
new TestIssuerNameService("https://idsrv.com"),
new DefaultReplayCache(new TestCache()),
new MockServerUrls() { Origin = "https://idsrv3.com" },
new IdentityServerOptions(),
new MockServerUrls() { Origin = "https://idsrv.com" },
_options,
new LoggerFactory().CreateLogger<PrivateKeyJwtSecretValidator>());

_clients = new InMemoryClientStore(ClientValidationTestClients.Get());
}

private JwtSecurityToken CreateToken(string clientId, DateTime? nowOverride = null, string aud = "https://idsrv3.com/connect/token")
private JwtSecurityToken CreateToken(string clientId, string aud = "https://idsrv.com/", DateTime? nowOverride = null)
{
return CreateTokenHelper(clientId, new Claim(JwtClaimTypes.Audience, aud), nowOverride);
}

private JwtSecurityToken CreateToken(string clientId, string[] audiences, DateTime? nowOverride = null)
{
return CreateTokenHelper(clientId, new Claim(JwtClaimTypes.Audience, JsonSerializer.Serialize(audiences), JsonClaimValueTypes.JsonArray), nowOverride);
}

private JwtSecurityToken CreateTokenHelper(string clientId, Claim aud = null, DateTime? nowOverride = null)
{
var certificate = TestCert.Load();
var now = nowOverride ?? DateTime.UtcNow;

aud ??= new Claim("aud", "https://idsrv.com");

var token = new JwtSecurityToken(
clientId,
aud,
null,
new List<Claim>()
{
new Claim("jti", Guid.NewGuid().ToString()),
new Claim(JwtClaimTypes.Subject, clientId),
new Claim(JwtClaimTypes.IssuedAt, new DateTimeOffset(now).ToUnixTimeSeconds().ToString(), ClaimValueTypes.Integer64)
new("jti", Guid.NewGuid().ToString()),
new(JwtClaimTypes.Subject, clientId),
new(JwtClaimTypes.IssuedAt, new DateTimeOffset(now).ToUnixTimeSeconds().ToString(), ClaimValueTypes.Integer64),
aud
},
now,
now.AddMinutes(1),
Expand Down Expand Up @@ -121,12 +137,12 @@ public async Task Valid_Certificate_Base64()
}

[Theory]
[InlineData("https://idsrv3.com")]
[InlineData("https://idsrv3.com/")]
[InlineData("https://idsrv3.com/connect/token")]
[InlineData("https://idsrv3.com/connect/ciba")]
[InlineData("https://idsrv3.com/connect/par")]
public async Task Valid_aud(string aud)
[InlineData("https://idsrv.com")]
[InlineData("https://idsrv.com/")]
[InlineData("https://idsrv.com/connect/token")]
[InlineData("https://idsrv.com/connect/ciba")]
[InlineData("https://idsrv.com/connect/par")]
public async Task Valid_legacy_aud(string aud)
{
var clientId = "certificate_base64_valid";
var client = await _clients.FindEnabledClientByIdAsync(clientId);
Expand All @@ -143,6 +159,78 @@ public async Task Valid_aud(string aud)
result.Success.Should().BeTrue();
}

[Theory]
[InlineData("https://idsrv.com", true)]
[InlineData("https://idsrv.com/", true)]
[InlineData("https://idsrv.com/connect/token", false)]
[InlineData("https://idsrv.com/connect/ciba", false)]
[InlineData("", false)]
[InlineData("https://idsrv.com/connect/par", false)]
public async Task Valid_strict_aud(string aud, bool expectSuccess)
{
_options.StrictClientAssertionAudienceValidation = true;

var clientId = "certificate_base64_valid";
var client = await _clients.FindEnabledClientByIdAsync(clientId);

var secret = new ParsedSecret
{
Id = clientId,
Credential = new JwtSecurityTokenHandler().WriteToken(CreateToken(clientId, aud:aud)),
Type = IdentityServerConstants.ParsedSecretTypes.JwtBearer
};

var result = await _validator.ValidateAsync(client.ClientSecrets, secret);

result.Success.Should().Be(expectSuccess, result.Error);
}

[Theory]
[InlineData("https://idsrv.com")]
[InlineData("https://idsrv.com/")]
[InlineData("https://idsrv.com/connect/token")]
[InlineData("https://idsrv.com/connect/ciba")]
[InlineData("https://idsrv.com/connect/par")]
public async Task StrictAudience_does_not_allow_single_valued_arrays(string aud)
{
_options.StrictClientAssertionAudienceValidation = true;

var clientId = "certificate_base64_valid";
var client = await _clients.FindEnabledClientByIdAsync(clientId);

var secret = new ParsedSecret
{
Id = clientId,
Credential = new JwtSecurityTokenHandler().WriteToken(CreateToken(clientId, [aud])),
Type = IdentityServerConstants.ParsedSecretTypes.JwtBearer
};

var result = await _validator.ValidateAsync(client.ClientSecrets, secret);

result.Success.Should().BeFalse();
}

[Fact]
public async Task StrictAudience_does_not_allow_multi_valued_arrays()
{
_options.StrictClientAssertionAudienceValidation = true;

var clientId = "certificate_base64_valid";
var client = await _clients.FindEnabledClientByIdAsync(clientId);

var secret = new ParsedSecret
{
Id = clientId,
Credential = new JwtSecurityTokenHandler().WriteToken(CreateToken(clientId,
["https://idsrv.com", "https://idsrv.com/"])),
Type = IdentityServerConstants.ParsedSecretTypes.JwtBearer
};

var result = await _validator.ValidateAsync(client.ClientSecrets, secret);

result.Success.Should().BeFalse();
}

[Fact]
public async Task Invalid_Replay()
{
Expand Down Expand Up @@ -230,7 +318,7 @@ public async Task Invalid_Expired_Token()
var clientId = "certificate_valid";
var client = await _clients.FindEnabledClientByIdAsync(clientId);

var token = CreateToken(clientId, DateTime.UtcNow.AddHours(-1));
var token = CreateToken(clientId, nowOverride: DateTime.UtcNow.AddHours(-1));
var secret = new ParsedSecret
{
Id = clientId,
Expand Down