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Allow OAuth provider hosts in CSP form-action #28

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Merged
murbard merged 1 commit into from
Jun 18, 2026
Merged

Allow OAuth provider hosts in CSP form-action #28

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7 changes: 7 additions & 0 deletions internal/web/csp_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -35,6 +35,13 @@ func TestCSPAllowsTemplateCDNs(t *testing.T) {
// Tailwind CDN fetches its CSS at runtime; without connect-src
// the page loads but stays unstyled.
{"connect-src", "https://cdn.tailwindcss.com"},
// form-action covers both the initial POST target AND any
// redirects from it. The reauth / OAuth-install flows POST
// same-origin and the server returns a 302 to the provider —
// without these hosts the redirect is blocked at the browser.
{"form-action", "https://accounts.google.com"},
{"form-action", "https://slack.com"},
{"form-action", "https://github.com"},
}
for _, want := range wants {
if !cspDirectiveContains(csp, want.directive, want.host) {
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13 changes: 12 additions & 1 deletion internal/web/headers.go
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Expand Up @@ -41,10 +41,21 @@ func WriteSensitive(w http.ResponseWriter) {
// connect-src also names these hosts because tailwindcss.com's runtime
// fetches its CSS via XHR; without that, the page loads but stays
// unstyled.
//
// form-action also names the OAuth-provider hosts the admin templates
// redirect form submissions to. CSP's form-action directive covers both
// the initial form target AND any redirects from that submission, so a
// POST to /connections/{id}/reauth (same-origin, allowed) that gets a
// 302 → accounts.google.com would otherwise be blocked at the redirect.
// Same applies to Slack OAuth (slack.com) and the GitHub App install /
// manifest flows (github.com). The list is intentionally minimal —
// adding a connector that POSTs to a new OAuth host requires updating
// this directive.
func writeSecurityHeaders(w http.ResponseWriter) {
const cdnScripts = "https://cdn.tailwindcss.com https://cdn.jsdelivr.net https://unpkg.com"
const cdnStyles = "https://fonts.googleapis.com"
const cdnFonts = "https://fonts.gstatic.com"
const oauthHosts = "https://accounts.google.com https://slack.com https://github.com"
h := w.Header()
h.Set("Content-Security-Policy",
"default-src 'self'; "+
Expand All @@ -56,7 +67,7 @@ func writeSecurityHeaders(w http.ResponseWriter) {
"object-src 'none'; "+
"frame-ancestors 'none'; "+
"base-uri 'none'; "+
"form-action 'self'")
"form-action 'self' "+oauthHosts)
h.Set("X-Frame-Options", "DENY")
h.Set("X-Content-Type-Options", "nosniff")
h.Set("Referrer-Policy", "no-referrer")
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