fix(oidc): prompts slice conversion function returns slice which contains unexpected empty strings (#8997)

# Which Problems Are Solved

Slice initialized with a fixed length instead of capacity, this leads to
unexpected results when calling the append function.

# How the Problems Are Solved

fixed slice initialization, slice is initialized with zero length and
with capacity of function's argument

# Additional Changes

test case added

# Additional Context
none

Co-authored-by: Kolokhanin Roman <zuzmic@gmail.com>
Co-authored-by: Tim Möhlmann <tim+github@zitadel.com>

internal/api/oidc/auth_request_converter.go

@@ -158,7 +158,7 @@ func IpFromContext(ctx context.Context) net.IP {
 }
 
 func PromptToBusiness(oidcPrompt []string) []domain.Prompt {
-	prompts := make([]domain.Prompt, len(oidcPrompt))
+	prompts := make([]domain.Prompt, 0, len(oidcPrompt))
 	for _, oidcPrompt := range oidcPrompt {
 		switch oidcPrompt {
 		case oidc.PromptNone:

internal/api/oidc/auth_request_converter_test.go

@@ -94,3 +94,36 @@ func TestResponseModeToOIDC(t *testing.T) {
 		})
 	}
 }
+
+func TestPromptToBusiness(t *testing.T) {
+	type args struct {
+		oidcPrompt []string
+	}
+	tests := []struct {
+		name string
+		args args
+		want []domain.Prompt
+	}{
+		{
+			name: "unspecified",
+			args: args{nil},
+			want: []domain.Prompt{},
+		},
+		{
+			name: "invalid",
+			args: args{[]string{"non_existing_prompt"}},
+			want: []domain.Prompt{},
+		},
+		{
+			name: "prompt_none",
+			args: args{[]string{oidc.PromptNone}},
+			want: []domain.Prompt{domain.PromptNone},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := PromptToBusiness(tt.args.oidcPrompt)
+			assert.Equal(t, tt.want, got)
+		})
+	}
+}