feat(backend-proxy-middleware): add property for additional url params

[heimwege]

Summary

• Add a params property to BaseBackendConfig in @sap-ux/backend-proxy-middleware as an officially supported way to append arbitrary query parameters to all proxied backend requests
• Add a warning when the client property is used to inject query parameters (e.g. "100&saml2=disabled"), guiding developers to use params instead
• Fixes the misuse described in client property in ui5.yaml can be misused to inject query parameters into backend URLs #4482

Problem

Developers working with backends that require additional query parameters (e.g. saml2=disabled to bypass SAML for Basic Auth flows) had no supported mechanism to append them. As a workaround, they injected parameters via the client property (e.g. client: "100&saml2=disabled"), which is fragile and undocumented.

Solution

New params property

  - name: backend-proxy-middleware
    afterMiddleware: compression
    configuration:
      backend:
        path: /sap
        url: https://my.backend.example:1234
        client: '100'
        params:
          saml2: disabled

The property is named params for consistency with UrlAbapTarget.params in @sap-ux/system-access, which serves the same purpose in the deploy task.

Client validation warning

When client contains a value that is not a 1–3 digit number, a warning is logged pointing to params as the correct
alternative. The existing workaround continues to function to avoid breaking existing projects.

[changeset-bot]

🦋 Changeset detected

Latest commit: 0dd220d

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@sap-ux/backend-proxy-middleware	Minor

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[longieirl]

Changeset is good.
Tests are good.
Change looks good.

[ytpo-lyne]

• changes to add url params look good
• changeset present
• coverage given
• tested manually, no issues found

Approving.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud