diff --git a/CHANGELOG.md b/CHANGELOG.md
index e02ee04de4..a9641d90c0 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,11 @@
 # Changelog
 
+### 0.5.1 (upcoming)
+
+* [PLT-3581] Add configurable sign-out URL via `--sign-out-url` / `OAUTH2_PROXY_SIGN_OUT_URL` to support non-standard IdP logout flows (e.g. Autentica/REDSARA)
+
+## Previous development
+
 ### 0.5.0 (2026-05-11)
 
 * [PLT-2583] Bump oauth2-proxy upstream to v7.15.2 (security fixes: authentication bypasses CVE-2026-34986, CVE-2026-32281 and others)
diff --git a/docs/docs/configuration/alpha_config.md b/docs/docs/configuration/alpha_config.md
index 680741bad5..5a77c4ba0d 100644
--- a/docs/docs/configuration/alpha_config.md
+++ b/docs/docs/configuration/alpha_config.md
@@ -574,6 +574,7 @@ Provider holds all configuration for a single provider
 | `googleConfig` | _[GoogleOptions](#googleoptions)_ | GoogleConfig holds all configurations for Google provider. |
 | `oidcConfig` | _[OIDCOptions](#oidcoptions)_ | OIDCConfig holds all configurations for OIDC provider<br/>or providers utilize OIDC configurations. |
 | `loginGovConfig` | _[LoginGovOptions](#logingovoptions)_ | LoginGovConfig holds all configurations for LoginGov provider. |
+| `sisConfig` | _[SISOptions](#sisoptions)_ | SISConfig holds all configurations for SIS provider. |
 | `id` | _string_ | ID should be a unique identifier for the provider.<br/>This value is required for all providers. |
 | `provider` | _[ProviderType](#providertype)_ | Type is the OAuth provider<br/>must be set from the supported providers group,<br/>otherwise 'Google' is set as default |
 | `name` | _string_ | Name is the providers display name<br/>if set, it will be shown to the users in the login page. |
@@ -592,6 +593,7 @@ Provider holds all configuration for a single provider
 | `code_challenge_method` | _string_ | The code challenge method |
 | `additionalClaims` | _[]string_ | Additional claims to be obtained from the upstream IDP, either from the id_token or from the userinfo endpoint if configured. |
 | `backendLogoutURL` | _string_ | URL to call to perform backend logout, `{id_token}` would be replaced by the actual `id_token` if available in the session |
+| `signOutURL` | _string_ | SignOutURL overrides the provider's default sign-out redirect URL |
 
 ### ProviderType
 #### (`string` alias)
@@ -615,6 +617,17 @@ AlphaConfig](https://oauth2-proxy.github.io/oauth2-proxy/configuration/alpha-con
 However, [**the feature to implement multiple providers is not
 complete**](https://github.com/oauth2-proxy/oauth2-proxy/issues/926).
 
+### SISOptions
+
+(**Appears on:** [Provider](#provider))
+
+
+
+| Field | Type | Description |
+| ----- | ---- | ----------- |
+| `SISRootURL` | _string_ | SISRootURL is the OpenID Connect SISRoot URL |
+| `ClearExtraCookieNames` | _[]string_ | ClearExtraCookieNames sets cookie names to clear after sign out |
+
 ### SecretSource
 
 (**Appears on:** [ClaimSource](#claimsource), [HeaderValue](#headervalue), [TLS](#tls))
diff --git a/pkg/apis/options/legacy_options.go b/pkg/apis/options/legacy_options.go
index ff7668b576..48f3996eb6 100644
--- a/pkg/apis/options/legacy_options.go
+++ b/pkg/apis/options/legacy_options.go
@@ -530,6 +530,7 @@ type LegacyProvider struct {
 	GoogleAdminAPIUserScope                string   `flag:"google-admin-api-user-scope" cfg:"google_admin_api_user_scope"`
 
 	SISRootURL            string   `flag:"sis-root-url" cfg:"sis_root_url"`
+	SignOutURL            string   `flag:"sign-out-url" cfg:"sign_out_url"`
 	ClearExtraCookieNames []string `flag:"clear-extra-cookie-names" cfg:"clear_extra_cookie_names"`
 
 	// These options allow for other providers besides Google, with
@@ -720,6 +721,7 @@ func (l *LegacyProvider) convert() (Providers, error) {
 		CodeChallengeMethod:      l.CodeChallengeMethod,
 		BackendLogoutURL:         l.BackendLogoutURL,
 		AuthRequestResponseMode:  l.AuthRequestResponseMode,
+		SignOutURL:               l.SignOutURL,
 	}
 
 	// This part is out of the switch section for all providers that support OIDC
diff --git a/pkg/apis/options/providers.go b/pkg/apis/options/providers.go
index a04dc2b37f..6fb71c69f8 100644
--- a/pkg/apis/options/providers.go
+++ b/pkg/apis/options/providers.go
@@ -141,6 +141,8 @@ type Provider struct {
 
 	// URL to call to perform backend logout, `{id_token}` would be replaced by the actual `id_token` if available in the session
 	BackendLogoutURL string `yaml:"backendLogoutURL"`
+	// SignOutURL overrides the provider's default sign-out redirect URL
+	SignOutURL string `yaml:"signOutURL,omitempty"`
 }
 
 // ProviderType is used to enumerate the different provider type options
diff --git a/providers/providers.go b/providers/providers.go
index 7e470ef691..7767fb3df9 100644
--- a/providers/providers.go
+++ b/providers/providers.go
@@ -137,6 +137,7 @@ func newProviderDataFromConfig(providerConfig options.Provider) (*ProviderData,
 		"profile":  {dst: &p.ProfileURL, raw: providerConfig.ProfileURL},
 		"validate": {dst: &p.ValidateURL, raw: providerConfig.ValidateURL},
 		"resource": {dst: &p.ProtectedResource, raw: providerConfig.ProtectedResource},
+		"signout":  {dst: &p.SignOutURL, raw: providerConfig.SignOutURL},
 	} {
 		var err error
 		*u.dst, err = url.Parse(u.raw)
diff --git a/providers/sis.go b/providers/sis.go
index 1c6163716a..dc9316ddf1 100644
--- a/providers/sis.go
+++ b/providers/sis.go
@@ -274,8 +274,8 @@ func (p *SISProvider) GetSignOutURL(redirectURI string) string {
 	// copy URL
 	redirect := *p.SignOutURL
 	if redirectURI != "" {
-		v := url.Values{}
-		v.Add("rd", redirectURI)
+		v := redirect.Query()
+		v.Set("rd", redirectURI)
 		redirect.RawQuery = v.Encode()
 	}
 	return redirect.String()
diff --git a/providers/sis_test.go b/providers/sis_test.go
index 0f305f59cd..329762926b 100644
--- a/providers/sis_test.go
+++ b/providers/sis_test.go
@@ -61,6 +61,41 @@ func TestSISProviderOverrides(t *testing.T) {
 	assert.Equal(t, "profile", p.Data().Scope)
 }
 
+func TestSISProviderGetSignOutURL(t *testing.T) {
+	tests := []struct {
+		name        string
+		signOutURL  string
+		redirectURI string
+		expected    string
+	}{
+		{
+			name:        "no redirect preserves sign-out URL as-is",
+			signOutURL:  "https://sis.example.com/sso/logout",
+			redirectURI: "",
+			expected:    "https://sis.example.com/sso/logout",
+		},
+		{
+			name:        "redirect appended as rd param",
+			signOutURL:  "https://sis.example.com/sso/logout",
+			redirectURI: "https://app.example.com/home",
+			expected:    "https://sis.example.com/sso/logout?rd=https%3A%2F%2Fapp.example.com%2Fhome",
+		},
+		{
+			name:        "existing query params preserved when adding rd",
+			signOutURL:  "https://autentica.example.com/logout?appId=5784",
+			redirectURI: "https://app.example.com/home",
+			expected:    "https://autentica.example.com/logout?appId=5784&rd=https%3A%2F%2Fapp.example.com%2Fhome",
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			u, _ := url.Parse(tt.signOutURL)
+			p := NewSISProvider(&ProviderData{SignOutURL: u}, options.SISOptions{})
+			assert.Equal(t, tt.expected, p.GetSignOutURL(tt.redirectURI))
+		})
+	}
+}
+
 func TestSISProviderRedeem(t *testing.T) {
 	b := testSISBackend(map[string]string{
 		"/sso/oauth2.0/accessToken": "access_token=imaginary_access_token&expires=10000",