diff --git a/pkg/apis/options/alpha_options.go b/pkg/apis/options/alpha_options.go
index 33daf17f..bd8cc229 100644
--- a/pkg/apis/options/alpha_options.go
+++ b/pkg/apis/options/alpha_options.go
@@ -74,4 +74,56 @@ func (a *AlphaOptions) MergeOptionsWithDefaults(opts *Options) {
 	opts.Server = a.Server
 	opts.MetricsServer = a.MetricsServer
 	opts.Providers = a.Providers
+
+	// Automatically add claims referenced in header injection to each
+	// provider's AdditionalClaims so they are extracted from the ID token.
+	collectHeaderClaimsIntoProviders(opts)
+}
+
+// builtinSessionClaims are claims that are always available on the session
+// without needing to be listed in AdditionalClaims.
+var builtinSessionClaims = map[string]bool{
+	"access_token":       true,
+	"id_token":           true,
+	"created_at":         true,
+	"expires_on":         true,
+	"refresh_token":      true,
+	"email":              true,
+	"user":               true,
+	"groups":             true,
+	"preferred_username": true,
+}
+
+// collectHeaderClaimsIntoProviders inspects InjectRequestHeaders and
+// InjectResponseHeaders for ClaimSource entries whose claim is not a
+// built-in session field and adds them to every provider's
+// AdditionalClaims list (deduplicated).
+func collectHeaderClaimsIntoProviders(opts *Options) {
+	needed := map[string]bool{}
+	for _, header := range append(opts.InjectRequestHeaders, opts.InjectResponseHeaders...) {
+		for _, value := range header.Values {
+			if value.ClaimSource != nil && value.ClaimSource.Claim != "" {
+				claim := value.ClaimSource.Claim
+				if !builtinSessionClaims[claim] {
+					needed[claim] = true
+				}
+			}
+		}
+	}
+
+	if len(needed) == 0 {
+		return
+	}
+
+	for i := range opts.Providers {
+		existing := map[string]bool{}
+		for _, c := range opts.Providers[i].AdditionalClaims {
+			existing[c] = true
+		}
+		for claim := range needed {
+			if !existing[claim] {
+				opts.Providers[i].AdditionalClaims = append(opts.Providers[i].AdditionalClaims, claim)
+			}
+		}
+	}
 }
diff --git a/pkg/apis/options/alpha_options_test.go b/pkg/apis/options/alpha_options_test.go
new file mode 100644
index 00000000..9e126040
--- /dev/null
+++ b/pkg/apis/options/alpha_options_test.go
@@ -0,0 +1,190 @@
+package options
+
+import (
+	"sort"
+
+	. "github.com/onsi/ginkgo/v2"
+	. "github.com/onsi/gomega"
+)
+
+var _ = Describe("AlphaOptions", func() {
+	Describe("collectHeaderClaimsIntoProviders", func() {
+		It("adds non-builtin claims from injectRequestHeaders to provider AdditionalClaims", func() {
+			opts := NewOptions()
+			opts.Providers = Providers{
+				{
+					ID:   "test",
+					Type: "oidc",
+				},
+			}
+			opts.InjectRequestHeaders = []Header{
+				{
+					Name: "X-Forwarded-Upn",
+					Values: []HeaderValue{
+						{ClaimSource: &ClaimSource{Claim: "upn"}},
+					},
+				},
+				{
+					Name: "X-Forwarded-GivenName",
+					Values: []HeaderValue{
+						{ClaimSource: &ClaimSource{Claim: "given_name"}},
+					},
+				},
+			}
+
+			collectHeaderClaimsIntoProviders(opts)
+
+			claims := opts.Providers[0].AdditionalClaims
+			sort.Strings(claims)
+			Expect(claims).To(ConsistOf("given_name", "upn"))
+		})
+
+		It("does not duplicate claims already in AdditionalClaims", func() {
+			opts := NewOptions()
+			opts.Providers = Providers{
+				{
+					ID:               "test",
+					Type:             "oidc",
+					AdditionalClaims: []string{"upn"},
+				},
+			}
+			opts.InjectRequestHeaders = []Header{
+				{
+					Name: "X-Forwarded-Upn",
+					Values: []HeaderValue{
+						{ClaimSource: &ClaimSource{Claim: "upn"}},
+					},
+				},
+			}
+
+			collectHeaderClaimsIntoProviders(opts)
+
+			Expect(opts.Providers[0].AdditionalClaims).To(Equal([]string{"upn"}))
+		})
+
+		It("skips builtin session claims", func() {
+			opts := NewOptions()
+			opts.Providers = Providers{
+				{
+					ID:   "test",
+					Type: "oidc",
+				},
+			}
+			opts.InjectRequestHeaders = []Header{
+				{
+					Name: "X-Email",
+					Values: []HeaderValue{
+						{ClaimSource: &ClaimSource{Claim: "email"}},
+					},
+				},
+				{
+					Name: "X-User",
+					Values: []HeaderValue{
+						{ClaimSource: &ClaimSource{Claim: "user"}},
+					},
+				},
+				{
+					Name: "X-Groups",
+					Values: []HeaderValue{
+						{ClaimSource: &ClaimSource{Claim: "groups"}},
+					},
+				},
+				{
+					Name: "X-Token",
+					Values: []HeaderValue{
+						{ClaimSource: &ClaimSource{Claim: "access_token"}},
+					},
+				},
+			}
+
+			collectHeaderClaimsIntoProviders(opts)
+
+			Expect(opts.Providers[0].AdditionalClaims).To(BeEmpty())
+		})
+
+		It("also collects claims from injectResponseHeaders", func() {
+			opts := NewOptions()
+			opts.Providers = Providers{
+				{
+					ID:   "test",
+					Type: "oidc",
+				},
+			}
+			opts.InjectResponseHeaders = []Header{
+				{
+					Name: "X-Family-Name",
+					Values: []HeaderValue{
+						{ClaimSource: &ClaimSource{Claim: "family_name"}},
+					},
+				},
+			}
+
+			collectHeaderClaimsIntoProviders(opts)
+
+			Expect(opts.Providers[0].AdditionalClaims).To(ConsistOf("family_name"))
+		})
+
+		It("adds claims to all providers", func() {
+			opts := NewOptions()
+			opts.Providers = Providers{
+				{
+					ID:   "provider1",
+					Type: "oidc",
+				},
+				{
+					ID:   "provider2",
+					Type: "oidc",
+				},
+			}
+			opts.InjectRequestHeaders = []Header{
+				{
+					Name: "X-Upn",
+					Values: []HeaderValue{
+						{ClaimSource: &ClaimSource{Claim: "upn"}},
+					},
+				},
+			}
+
+			collectHeaderClaimsIntoProviders(opts)
+
+			Expect(opts.Providers[0].AdditionalClaims).To(ConsistOf("upn"))
+			Expect(opts.Providers[1].AdditionalClaims).To(ConsistOf("upn"))
+		})
+
+		It("ignores headers with only SecretSource values", func() {
+			opts := NewOptions()
+			opts.Providers = Providers{
+				{
+					ID:   "test",
+					Type: "oidc",
+				},
+			}
+			opts.InjectRequestHeaders = []Header{
+				{
+					Name: "X-Static",
+					Values: []HeaderValue{
+						{SecretSource: &SecretSource{Value: []byte("static-value")}},
+					},
+				},
+			}
+
+			collectHeaderClaimsIntoProviders(opts)
+
+			Expect(opts.Providers[0].AdditionalClaims).To(BeEmpty())
+		})
+
+		It("does nothing when no headers are configured", func() {
+			opts := NewOptions()
+			opts.Providers = Providers{
+				{
+					ID:   "test",
+					Type: "oidc",
+				},
+			}
+
+			collectHeaderClaimsIntoProviders(opts)
+
+			Expect(opts.Providers[0].AdditionalClaims).To(BeNil())
+		})
+	})
+})