OSCrypt for POSIX uses libsecret to store a randomised encryption key.

components/os_crypt/BUILD.gn

Index: components/os_crypt/BUILD.gn
diff --git a/components/os_crypt/BUILD.gn b/components/os_crypt/BUILD.gn
index 6e37c63c8c280dead73a9d623ee963300ae0db4d..3845bace61d56ceb138f689502da2b65a35db441 100644
--- a/components/os_crypt/BUILD.gn
+++ b/components/os_crypt/BUILD.gn
@@ -42,9 +42,13 @@ source_set("os_crypt") {
   }
 
   if (is_desktop_linux) {
+    sources -= [ "os_crypt_posix.cc" ]
     sources += [
+      "key_storage_linux.cc",
+      "key_storage_linux.h",
       "libsecret_util_posix.cc",
       "libsecret_util_posix.h",
+      "os_crypt_linux.cc",
     ]
     configs += [ "//build/config/linux:glib" ]
     deps += [ "//third_party/libsecret" ]
@@ -65,4 +69,10 @@ source_set("unit_tests") {
     "//crypto",
     "//testing/gtest",
   ]
+
+  if (is_desktop_linux) {
+    sources += [ "os_crypt_util_linux_unittest.cc" ]
+    deps += [ "//third_party/libsecret" ]
+    defines = [ "USE_LIBSECRET" ]
+  }
 }