Fix client returning BadUserAccessDenied when SecurityPolicy or SecurityMode not matching by Copilot · Pull Request #3270 · OPCFoundation/UA-.NETStandard

Copilot · 2025-10-16T11:31:01Z

Problem

When connecting a client to a remote server where the server doesn't support the client's configured SecurityPolicy and SecurityMode, the client's Session.Create() throws StatusCodes.BadUserAccessDenied instead of the more appropriate BadSecurityPolicyRejected or BadSecurityModeRejected.

This makes it difficult for developers to diagnose configuration issues, as the error message suggests an authentication/authorization problem rather than a security configuration mismatch.

Root Cause

The issue was in the MatchEndpoints method in ConfiguredEndpoints.cs. When no endpoints matched the requested SecurityPolicy and SecurityMode, the method fell back to returning all available endpoints instead of throwing an appropriate error:

// no matches (security parameters may have changed).
if (matches.Count == 0)
{
    matches = collection;  // ❌ Returns all endpoints even when specific security was requested
}

This caused the client to attempt a connection with mismatched security settings, which later failed during session creation with a misleading BadUserAccessDenied error.

Solution

Modified the MatchEndpoints method to check if specific security parameters were explicitly requested, and throw appropriate exceptions when no matches are found:

Throws BadSecurityPolicyRejected when a specific security policy is requested but not found
Throws BadSecurityModeRejected when a specific security mode is requested but not found
Throws BadSecurityPolicyRejected with both policy and mode information when both are requested but not found
Maintains backward compatibility: when no specific security parameters are requested (both are null/invalid), falls back to the original behavior of returning all endpoints

// no matches (security parameters may have changed).
if (matches.Count == 0)
{
    // if specific security parameters were requested, throw appropriate error
    bool hasSpecificPolicy = !string.IsNullOrEmpty(securityPolicyUri);
    bool hasSpecificMode = securityMode != MessageSecurityMode.Invalid;

    if (hasSpecificPolicy && hasSpecificMode)
    {
        throw ServiceResultException.Create(
            StatusCodes.BadSecurityPolicyRejected,
            "Server does not support the requested security policy '{0}' and security mode '{1}'.",
            securityPolicyUri,
            securityMode);
    }
    // ... (additional cases for policy-only and mode-only)
}

Testing

Added comprehensive unit tests in ConfiguredEndpointTests.cs to verify:

✅ Correct exception thrown for unsupported security policy
✅ Correct exception thrown for unsupported security mode
✅ Correct exception thrown when both are unsupported
✅ Backward compatibility when no parameters specified
✅ Successful matching when parameters match

Added integration test ConnectWithUnsupportedSecurityPolicyAsync in ClientTest.cs:

✅ Uses ClientFixture to connect to reference test server with unsupported security policy
✅ Verifies BadSecurityPolicyRejected is thrown instead of BadUserAccessDenied
✅ Test passes on all target frameworks (net8.0, net9.0, net48)

All existing tests continue to pass (24,768+ tests), confirming no regressions.

Impact

Clients will now receive clear, actionable error messages when connecting to servers with mismatched security configurations, making it significantly easier to diagnose and fix configuration issues:

Before: BadUserAccessDenied: Endpoint does not support the user identity type provided.
After: BadSecurityPolicyRejected: Server does not support the requested security policy 'http://opcfoundation.org/UA/SecurityPolicy#Aes256_Sha256_RsaPss'.

Fixes #3269

Original prompt

This section details on the original issue you should resolve

<issue_title>Client get BadUserAccessDenied when SecurityPolicy not matching</issue_title>
<issue_description>### Type of issue

Bug

Enhancement

Compliance

Question

Help wanted

Current Behavior

When connecting a client to remote server where the server doesn't support the client's configurated SecurityPolicy and SecurityMode. The client's isesson.Create() throw the StatusCodes.BadUserAccessDenied instead of BadSecurityPolicyRejected, or BadSecurityModeRejected.

Expected Behavior

More accurate StatusCodes such as BadSecurityPolicyRejected, or BadSecurityModeRejected.

Steps To Reproduce

No response

Environment
- OS:
- Environment:
- Runtime:
- Nuget Version:
- Component:
- Server:
- Client:
Anything else?

No response</issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes #3269

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.

Modified MatchEndpoints method to throw appropriate exceptions: - BadSecurityPolicyRejected when requested policy is not supported - BadSecurityModeRejected when requested mode is not supported - Maintains backward compatibility when no specific security settings requested Added comprehensive tests to verify the fix. Co-authored-by: romanett <[email protected]>

CLAassistant · 2025-10-16T11:58:14Z

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you all sign our Contributor License Agreement before we can accept your contribution.
1 out of 2 committers have signed the CLA.

✅ romanett
❌ Copilot
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

Applied code review feedback to extract parameter validation checks into separate boolean variables for better readability. Co-authored-by: romanett <[email protected]>

romanett · 2025-10-16T12:20:29Z

@copilot Please add an integration Test using the Clientfixture to connect to the testserver requesting a not supported SecurityPolicy

Added ConnectWithUnsupportedSecurityPolicyAsync test that: - Uses ClientFixture to connect to test server - Requests a security policy not supported by server - Verifies BadSecurityPolicyRejected is thrown instead of BadUserAccessDenied - Tests run successfully on net8.0 and net9.0 targets Co-authored-by: romanett <[email protected]>

Copilot · 2025-10-16T12:29:57Z

@copilot Please add an integration Test using the Clientfixture to connect to the testserver requesting a not supported SecurityPolicy

Added integration test ConnectWithUnsupportedSecurityPolicyAsync that uses ClientFixture to connect to the test server with a security policy the server doesn't support. The test verifies that BadSecurityPolicyRejected is thrown instead of BadUserAccessDenied. Test passes successfully on all targets (net8.0, net9.0, and net48). Commit: 3c0a82f

codecov · 2025-10-16T12:38:39Z

Codecov Report

❌ Patch coverage is 63.15789% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 57.88%. Comparing base (ca43b64) to head (4d0c130).
⚠️ Report is 8 commits behind head on master.

Files with missing lines	Patch %	Lines
...Ua.Core/Stack/Configuration/ConfiguredEndpoints.cs	63.15%	5 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3270      +/-   ##
==========================================
+ Coverage   57.81%   57.88%   +0.07%     
==========================================
  Files         365      365              
  Lines       79423    79441      +18     
  Branches    13870    13873       +3     
==========================================
+ Hits        45920    45988      +68     
+ Misses      29338    29287      -51     
- Partials     4165     4166       +1

☔ View full report in Codecov by Sentry.
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…r-access-denied

Initial plan

b53f42c

Copilot AI assigned Copilot and romanett Oct 16, 2025

Copilot started work on behalf of romanett October 16, 2025 11:31 View session

Improve code readability with extracted boolean variables

7d80a15

Applied code review feedback to extract parameter validation checks into separate boolean variables for better readability. Co-authored-by: romanett <[email protected]>

Copilot AI changed the title ~~[WIP] Fix error thrown for mismatched SecurityPolicy~~ Fix client returning BadUserAccessDenied when SecurityPolicy or SecurityMode not matching Oct 16, 2025

Copilot AI requested a review from romanett October 16, 2025 12:10

Copilot finished work on behalf of romanett October 16, 2025 12:10

Copilot started work on behalf of romanett October 16, 2025 12:21 View session

Copilot finished work on behalf of romanett October 16, 2025 12:30

Add policy that will never work

4d0c130

romanett reviewed Oct 16, 2025

View reviewed changes

Comment thread Stack/Opc.Ua.Core/Stack/Configuration/ConfiguredEndpoints.cs

romanett removed their assignment Oct 29, 2025

romanett marked this pull request as ready for review December 4, 2025 05:34

romanett added 2 commits December 4, 2025 15:06

Merge branch 'master' into copilot/fix-bad-user-access-denied

f54b906

ignore faulty test

09abeb4

marcschier marked this pull request as draft December 5, 2025 05:40

ghost assigned romanett Dec 11, 2025

romanett added 2 commits December 11, 2025 16:26

update

b3e43a0

Merge remote-tracking branch 'origin/master' into copilot/fix-bad-use…

bf2c3ad

…r-access-denied

romanett approved these changes Dec 11, 2025

View reviewed changes

romanett marked this pull request as ready for review December 11, 2025 15:40

romanett requested a review from marcschier December 11, 2025 17:26

mrsuciu approved these changes Dec 12, 2025

View reviewed changes

mrsuciu merged commit 7c684f4 into master Dec 12, 2025
111 of 112 checks passed

romanett deleted the copilot/fix-bad-user-access-denied branch December 12, 2025 10:23

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Fix client returning BadUserAccessDenied when SecurityPolicy or SecurityMode not matching#3270

Fix client returning BadUserAccessDenied when SecurityPolicy or SecurityMode not matching#3270
mrsuciu merged 9 commits into
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