feat: add RedirectUriPrefix support to OpenIdConnectConfiguration for sub-path deployments

[IbrahimNadaa]

Purpose

Allow applications using the ElsaLogin OIDC flow to configure a path prefix for the redirect_uri,
enabling correct authentication in sub-path deployments where the IdP enforces a specific redirect_uri format.

Scope

Select one primary concern:

• Bug fix (behavior change)
• Refactor (no behavior change)
• Documentation update
• Formatting / code cleanup
• Dependency / build update
• New feature

If this PR includes multiple unrelated concerns, please split it before requesting review.

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This produces https://myapp.com/workflow/signin-oidc instead of https://myapp.com/signin-oidc.
When not set, behaviour is unchanged — defaults to {origin}/signin-oidc.

---

Verification

Steps:

1. Deploy or configure the Elsa Studio host behind a reverse proxy or sub-path (e.g., /workflow).
2. Set Authentication:ElsaLogin:RedirectUriPrefix to /workflow in appsettings.json.
3. Register https://myapp.com/workflow/signin-oidc as an allowed redirect URI in your IdP
   (e.g., Azure AD, Keycloak).
4. Navigate to Elsa Studio and trigger the OIDC login flow.

Expected outcome: The authorization request is sent with
redirect_uri=https://myapp.com/workflow/signin-oidc, the IdP accepts it, and the user is
successfully authenticated.

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Screenshots / Recordings (if applicable)

N/A — No UI changes. This is a configuration and service-layer change only.

---

Checklist

• The PR is focused on a single concern
• Commit messages follow the recommended convention
• Tests added or updated (if applicable)
• Documentation updated (if applicable)
• No unrelated cleanup included
• All tests pass

[greptile-apps]

Greptile Summary

This PR adds a RedirectUriPrefix property to OpenIdConnectConfiguration so that Elsa Studio OIDC flows work correctly behind a reverse proxy or sub-path deployment (e.g., /workflow). A new StringExtensions helper normalises the prefix and both RedirectToAuthorizationServer and ReceiveAuthorizationCode are updated consistently.

• RedirectUriPrefix is optional and null-safe; when unset the existing {origin}/signin-oidc behaviour is preserved.
• An unrelated encoding regression was introduced while stripping the BOM: the HORIZONTAL ELLIPSIS \u2026 (U+2026) on line 136 of OpenIdConnectAuthorizationService.cs was corrupted to the Unicode Replacement Character (U+FFFD), which will garble truncated error log entries.
• EnsureEndsWith in StringExtensions.cs is defined but never called.

Confidence Score: 4/5

Safe to merge after fixing the corrupted ellipsis character in the error-logging path; the OIDC feature itself is correctly implemented.

The redirect URI construction change is correct and backward-compatible. The one concrete defect is an unintended character corruption on line 136 of OpenIdConnectAuthorizationService.cs — the ellipsis was replaced with the Unicode Replacement Character when the BOM was stripped, meaning every truncated OIDC error log entry will end with a garbled glyph.

src/modules/Elsa.Studio.Login/Services/OpenIdConnectAuthorizationService.cs — specifically line 136 where the ellipsis character was corrupted.

Important Files Changed

Filename	Overview
src/modules/Elsa.Studio.Login/Services/OpenIdConnectAuthorizationService.cs	Adds RedirectUriPrefix support to redirect URI construction; inadvertently corrupts the ellipsis character (U+2026 to U+FFFD) in ReadErrorSummaryAsync line 136 due to BOM removal.
src/modules/Elsa.Studio.Login/Extensions/StringExtensions.cs	New helper file adding EnsureStartsWith and EnsureEndsWith string extensions; EnsureEndsWith is currently unused dead code.
src/modules/Elsa.Studio.Login/Models/OpenIdConnectConfiguration.cs	Adds nullable RedirectUriPrefix property with clear XML doc comment; no issues.

Sequence Diagram

sequenceDiagram
    participant Browser
    participant ElsaStudio as Elsa Studio (Blazor)
    participant Config as OpenIdConnectConfiguration
    participant IdP as Identity Provider

    Browser->>ElsaStudio: Navigate to protected route
    ElsaStudio->>Config: Read RedirectUriPrefix (e.g. "/workflow")
    ElsaStudio->>ElsaStudio: "Build redirectUri = origin + EnsureStartsWith + /signin-oidc"
    Note over ElsaStudio: e.g. https://myapp.com/workflow/signin-oidc
    ElsaStudio->>IdP: GET /authorize with redirect_uri
    IdP-->>Browser: 302 to redirect_uri with auth code
    Browser->>ElsaStudio: "GET /workflow/signin-oidc?code=AUTH_CODE"
    ElsaStudio->>Config: Read RedirectUriPrefix again
    ElsaStudio->>ElsaStudio: Rebuild same redirectUri for token exchange
    ElsaStudio->>IdP: POST /token with code and redirect_uri
    IdP-->>ElsaStudio: access_token, refresh_token, id_token
    ElsaStudio-->>Browser: NavigateTo returnUrl

Loading

Prompt To Fix All With AI

Fix the following 2 code review issues. Work through them one at a time, proposing concise fixes.

---

### Issue 1 of 2
src/modules/Elsa.Studio.Login/Extensions/StringExtensions.cs:19-28
`EnsureEndsWith` is defined but never called anywhere in this PR or the existing codebase. Shipping unused internal code creates unnecessary maintenance surface. If it's genuinely needed in a follow-up, it can be added then; otherwise it should be removed.

### Issue 2 of 2
src/modules/Elsa.Studio.Login/Services/OpenIdConnectAuthorizationService.cs:136
**Corrupted ellipsis character**

The original file (which had a UTF-8 BOM) contained the HORIZONTAL ELLIPSIS `…` (U+2026) on this line. When the BOM was stripped in this PR, the multi-byte sequence for that character was corrupted to U+FFFD (the Unicode Replacement Character). At runtime, truncated error summaries logged by `ReadErrorSummaryAsync` will end with the replacement character `<?>` instead of `…`, producing garbled log output. Replace the character literal on this line with the correct `…` (U+2026), or use the escape `\u2026`.

_{Reviews (2): Last reviewed commit: "Merge branch 'main' into feat-adding-Red..." | Re-trigger Greptile}

[IbrahimNadaa]

@sfmskywalker
please take a look at this PR

[sfmskywalker]

@greptile please review

[greptile-apps]

Corrupted ellipsis character

The original file (which had a UTF-8 BOM) contained the HORIZONTAL ELLIPSIS … (U+2026) on this line. When the BOM was stripped in this PR, the multi-byte sequence for that character was corrupted to U+FFFD (the Unicode Replacement Character). At runtime, truncated error summaries logged by ReadErrorSummaryAsync will end with the replacement character <?> instead of …, producing garbled log output. Replace the character literal on this line with the correct … (U+2026), or use the escape \u2026.

Prompt To Fix With AI

This is a comment left during a code review.
Path: src/modules/Elsa.Studio.Login/Services/OpenIdConnectAuthorizationService.cs
Line: 136

Comment:
**Corrupted ellipsis character**

The original file (which had a UTF-8 BOM) contained the HORIZONTAL ELLIPSIS `…` (U+2026) on this line. When the BOM was stripped in this PR, the multi-byte sequence for that character was corrupted to U+FFFD (the Unicode Replacement Character). At runtime, truncated error summaries logged by `ReadErrorSummaryAsync` will end with the replacement character `<?>` instead of `…`, producing garbled log output. Replace the character literal on this line with the correct `…` (U+2026), or use the escape `\u2026`.

How can I resolve this? If you propose a fix, please make it concise.

[greptile-apps]

PR author is not in the allowed authors list.

[IbrahimNadaa]

appreciate the wonderful package, any update on this we really need this feature

[IbrahimNadaa]

any updates on this?

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