diff --git a/src/libcmd/command.cc b/src/libcmd/command.cc
index 543250da3..5b6820841 100644
--- a/src/libcmd/command.cc
+++ b/src/libcmd/command.cc
@@ -75,28 +75,32 @@ CopyCommand::CopyCommand()
         .longName = "from",
         .description = "URL of the source Nix store.",
         .labels = {"store-uri"},
-        .handler = {&srcUri},
+        .handler = {[&](std::string storeUri) {
+            srcUri = StoreReference::parse(storeUri);
+        }},
     });
 
     addFlag({
         .longName = "to",
         .description = "URL of the destination Nix store.",
         .labels = {"store-uri"},
-        .handler = {&dstUri},
+        .handler = {[&](std::string storeUri) {
+            dstUri = StoreReference::parse(storeUri);
+        }},
     });
 }
 
 ref<Store> CopyCommand::createStore()
 {
-    return srcUri.empty() ? StoreCommand::createStore() : openStore(srcUri);
+    return !srcUri ? StoreCommand::createStore() : openStore(*srcUri);
 }
 
 ref<Store> CopyCommand::getDstStore()
 {
-    if (srcUri.empty() && dstUri.empty())
+    if (!srcUri && !dstUri)
         throw UsageError("you must pass '--from' and/or '--to'");
 
-    return dstUri.empty() ? openStore() : openStore(dstUri);
+    return !dstUri ? openStore() : openStore(*dstUri);
 }
 
 EvalCommand::EvalCommand()
diff --git a/src/libcmd/command.hh b/src/libcmd/command.hh
index 4a72627ed..4628832b6 100644
--- a/src/libcmd/command.hh
+++ b/src/libcmd/command.hh
@@ -62,7 +62,7 @@ private:
  */
 struct CopyCommand : virtual StoreCommand
 {
-    std::string srcUri, dstUri;
+    std::optional<StoreReference> srcUri, dstUri;
 
     CopyCommand();
 
diff --git a/src/libcmd/common-eval-args.cc b/src/libcmd/common-eval-args.cc
index 155b43b70..084c5eb00 100644
--- a/src/libcmd/common-eval-args.cc
+++ b/src/libcmd/common-eval-args.cc
@@ -164,7 +164,9 @@ MixEvalArgs::MixEvalArgs()
           )",
         .category = category,
         .labels = {"store-url"},
-        .handler = {&evalStoreUrl},
+        .handler = {[&](std::string s) {
+            evalStoreUrl = StoreReference::parse(s);
+        }},
     });
 }
 
diff --git a/src/libcmd/common-eval-args.hh b/src/libcmd/common-eval-args.hh
index 75cb19334..fd06e1415 100644
--- a/src/libcmd/common-eval-args.hh
+++ b/src/libcmd/common-eval-args.hh
@@ -5,6 +5,7 @@
 #include "canon-path.hh"
 #include "common-args.hh"
 #include "search-path.hh"
+#include "store-reference.hh"
 
 #include <filesystem>
 
@@ -25,7 +26,7 @@ struct MixEvalArgs : virtual Args, virtual MixRepair
 
     LookupPath lookupPath;
 
-    std::optional<std::string> evalStoreUrl;
+    std::optional<StoreReference> evalStoreUrl;
 
 private:
     struct AutoArgExpr { std::string expr; };
diff --git a/src/libexpr/flake/flake.cc b/src/libexpr/flake/flake.cc
index 3af9ef14e..e9cb6a61b 100644
--- a/src/libexpr/flake/flake.cc
+++ b/src/libexpr/flake/flake.cc
@@ -1,3 +1,5 @@
+#include <nlohmann/json.hpp>
+
 #include "terminal.hh"
 #include "flake.hh"
 #include "eval.hh"
diff --git a/src/libexpr/primops/fetchClosure.cc b/src/libexpr/primops/fetchClosure.cc
index fc5bb3145..114422a8f 100644
--- a/src/libexpr/primops/fetchClosure.cc
+++ b/src/libexpr/primops/fetchClosure.cc
@@ -182,23 +182,26 @@ static void prim_fetchClosure(EvalState & state, const PosIdx pos, Value * * arg
             .pos = state.positions[pos]
         });
 
-    auto parsedURL = parseURL(*fromStoreUrl);
+    auto parsedURL = StoreReference::parse(*fromStoreUrl);
 
-    if (parsedURL.scheme != "http" &&
-        parsedURL.scheme != "https" &&
-        !(getEnv("_NIX_IN_TEST").has_value() && parsedURL.scheme == "file"))
+    auto * storeVariant = std::get_if<StoreReference::Specified>(&parsedURL.variant);
+
+    if (!storeVariant ||
+        (storeVariant->scheme != "http" &&
+         storeVariant->scheme != "https" &&
+         !(getEnv("_NIX_IN_TEST").has_value() && storeVariant->scheme == "file")))
         throw Error({
             .msg = HintFmt("'fetchClosure' only supports http:// and https:// stores"),
             .pos = state.positions[pos]
         });
 
-    if (!parsedURL.query.empty())
+    if (!parsedURL.params.empty())
         throw Error({
             .msg = HintFmt("'fetchClosure' does not support URL query parameters (in '%s')", *fromStoreUrl),
             .pos = state.positions[pos]
         });
 
-    auto fromStore = openStore(parsedURL.to_string());
+    auto fromStore = openStore(parsedURL);
 
     if (toPath)
         runFetchClosureWithRewrite(state, pos, *fromStore, *fromPath, *toPath, v);
diff --git a/src/libexpr/primops/fetchTree.cc b/src/libexpr/primops/fetchTree.cc
index fa462dc33..557aa78d2 100644
--- a/src/libexpr/primops/fetchTree.cc
+++ b/src/libexpr/primops/fetchTree.cc
@@ -15,6 +15,8 @@
 #include <iomanip>
 #include <regex>
 
+#include <nlohmann/json.hpp>
+
 namespace nix {
 
 void emitTreeAttrs(
diff --git a/src/libfetchers/unix/git.cc b/src/libfetchers/unix/git.cc
index fa7ef3621..7544c4c09 100644
--- a/src/libfetchers/unix/git.cc
+++ b/src/libfetchers/unix/git.cc
@@ -13,6 +13,7 @@
 #include "git-utils.hh"
 #include "logging.hh"
 #include "finally.hh"
+#include "json-utils.hh"
 
 #include "fetch-settings.hh"
 
diff --git a/src/libstore-c/nix_api_store.cc b/src/libstore-c/nix_api_store.cc
index 4fe25c7d4..2f8616c41 100644
--- a/src/libstore-c/nix_api_store.cc
+++ b/src/libstore-c/nix_api_store.cc
@@ -49,14 +49,15 @@ Store * nix_store_open(nix_c_context * context, const char * uri, const char ***
         if (uri_str.empty())
             return new Store{nix::openStore()};
 
-        if (!params)
-            return new Store{nix::openStore(uri_str)};
+        auto base_uri = nix::StoreReference::parse(uri_str);
 
-        nix::Store::Params params_map;
-        for (size_t i = 0; params[i] != nullptr; i++) {
-            params_map[params[i][0]] = params[i][1];
+        if (params) {
+            for (size_t i = 0; params[i] != nullptr; i++) {
+                base_uri.params[params[i][0]] = params[i][1];
+            }
         }
-        return new Store{nix::openStore(uri_str, params_map)};
+
+        return new Store{nix::openStore(std::move(base_uri))};
     }
     NIXC_CATCH_ERRS_NULL
 }
diff --git a/src/libstore/daemon.cc b/src/libstore/daemon.cc
index 47d6d5541..029669461 100644
--- a/src/libstore/daemon.cc
+++ b/src/libstore/daemon.cc
@@ -215,22 +215,22 @@ struct ClientSettings
             auto & name(i.first);
             auto & value(i.second);
 
-            auto setSubstituters = [&](Setting<Strings> & res) {
+            auto setSubstituters = [&](Setting<std::vector<StoreReference>> & res) {
                 if (name != res.name && res.aliases.count(name) == 0)
                     return false;
-                StringSet trusted = settings.trustedSubstituters;
+                std::set<StoreReference> trusted = settings.trustedSubstituters;
                 for (auto & s : settings.substituters.get())
                     trusted.insert(s);
-                Strings subs;
+                std::vector<StoreReference> subs;
                 auto ss = tokenizeString<Strings>(value);
-                for (auto & s : ss)
-                    if (trusted.count(s))
-                        subs.push_back(s);
-                    else if (!hasSuffix(s, "/") && trusted.count(s + "/"))
-                        subs.push_back(s + "/");
+                for (auto & s : ss) {
+                    auto ref = StoreReference::parse(s);
+                    if (trusted.count(ref))
+                        subs.push_back(ref);
                     else
                         warn("ignoring untrusted substituter '%s', you are not a trusted user.\n"
                              "Run `man nix.conf` for more information on the `substituters` configuration option.", s);
+                }
                 res = subs;
                 return true;
             };
diff --git a/src/libstore/derivations.cc b/src/libstore/derivations.cc
index e13705911..99c2e08db 100644
--- a/src/libstore/derivations.cc
+++ b/src/libstore/derivations.cc
@@ -1,3 +1,6 @@
+#include <boost/container/small_vector.hpp>
+#include <nlohmann/json.hpp>
+
 #include "derivations.hh"
 #include "downstream-placeholder.hh"
 #include "store-api.hh"
@@ -7,8 +10,7 @@
 #include "split.hh"
 #include "common-protocol.hh"
 #include "common-protocol-impl.hh"
-#include <boost/container/small_vector.hpp>
-#include <nlohmann/json.hpp>
+#include "json-utils.hh"
 
 namespace nix {
 
diff --git a/src/libstore/globals.cc b/src/libstore/globals.cc
index d9cab2fb8..d81229e27 100644
--- a/src/libstore/globals.cc
+++ b/src/libstore/globals.cc
@@ -35,6 +35,10 @@
 
 namespace nix {
 
+DECLARE_CONFIG_SERIALISER(StoreReference)
+DECLARE_CONFIG_SERIALISER(std::optional<StoreReference>)
+DECLARE_CONFIG_SERIALISER(std::set<StoreReference>)
+DECLARE_CONFIG_SERIALISER(std::vector<StoreReference>)
 
 /* The default location of the daemon socket, relative to nixStateDir.
    The socket is in a directory to allow you to control access to the
@@ -319,6 +323,66 @@ template<> void BaseSetting<SandboxMode>::convertToArg(Args & args, const std::s
     });
 }
 
+template<> StoreReference BaseSetting<StoreReference>::parse(const std::string & str) const
+{
+    return StoreReference::parse(str);
+}
+
+template<> std::string BaseSetting<StoreReference>::to_string() const
+{
+    return value.render();
+}
+
+template<> std::optional<StoreReference> BaseSetting<std::optional<StoreReference>>::parse(const std::string & str) const
+{
+    if (str == "")
+        return std::nullopt;
+    else
+        return StoreReference::parse(str);
+}
+
+template<> std::string BaseSetting<std::optional<StoreReference>>::to_string() const
+{
+    return value ? value->render() : "";
+}
+
+template<> std::set<StoreReference> BaseSetting<std::set<StoreReference>>::parse(const std::string & str) const
+{
+    std::set<StoreReference> res;
+    for (const auto & s : tokenizeString<std::vector<std::string>>(str))
+        res.insert(StoreReference::parse(s));
+    return res;
+}
+
+template<> std::string BaseSetting<std::set<StoreReference>>::to_string() const
+{
+    std::set<std::string> strings;
+    for (const auto & ref : value)
+        strings.insert(ref.render());
+    return concatStringsSep(" ", strings);
+}
+
+template<> std::vector<StoreReference> BaseSetting<std::vector<StoreReference>>::parse(const std::string & str) const
+{
+    std::vector<StoreReference> res;
+    for (const auto & s : tokenizeString<std::vector<std::string>>(str))
+        res.push_back(StoreReference::parse(s));
+    return res;
+}
+
+template<> std::string BaseSetting<std::vector<StoreReference>>::to_string() const
+{
+    std::vector<std::string> strings;
+    for (const auto & ref : value)
+        strings.push_back(ref.render());
+    return concatStringsSep(" ", strings);
+}
+
+template class BaseSetting<StoreReference>;
+template class BaseSetting<std::optional<StoreReference>>;
+template class BaseSetting<std::set<StoreReference>>;
+template class BaseSetting<std::vector<StoreReference>>;
+
 unsigned int MaxBuildJobsSetting::parse(const std::string & str) const
 {
     if (str == "auto") return std::max(1U, std::thread::hardware_concurrency());
diff --git a/src/libstore/globals.hh b/src/libstore/globals.hh
index dc18a11fc..cf0e2fbea 100644
--- a/src/libstore/globals.hh
+++ b/src/libstore/globals.hh
@@ -5,6 +5,7 @@
 #include "config.hh"
 #include "environment-variables.hh"
 #include "experimental-features.hh"
+#include "store-reference.hh"
 #include "users.hh"
 
 #include <map>
@@ -116,7 +117,7 @@ public:
      */
     Path nixDaemonSocketFile;
 
-    Setting<std::string> storeUri{this, getEnv("NIX_REMOTE").value_or("auto"), "store",
+    Setting<StoreReference> storeUri{this, StoreReference::parse(getEnv("NIX_REMOTE").value_or("auto")), "store",
         R"(
           The [URL of the Nix store](@docroot@/store/types/index.md#store-url-format)
           to use for most operations.
@@ -904,9 +905,16 @@ public:
         // Don't document the machine-specific default value
         false};
 
-    Setting<Strings> substituters{
+    Setting<std::vector<StoreReference>> substituters{
         this,
-        Strings{"https://cache.nixos.org/"},
+        {
+            {
+                .variant = StoreReference::Specified {
+                    .scheme = "https",
+                    .authority = "cache.nixos.org",
+                },
+            },
+        },
         "substituters",
         R"(
           A list of [URLs of Nix stores](@docroot@/store/types/index.md#store-url-format) to be used as substituters, separated by whitespace.
@@ -925,7 +933,7 @@ public:
         )",
         {"binary-caches"}};
 
-    Setting<StringSet> trustedSubstituters{
+    Setting<std::set<StoreReference>> trustedSubstituters{
         this, {}, "trusted-substituters",
         R"(
           A list of [Nix store URLs](@docroot@/store/types/index.md#store-url-format), separated by whitespace.
diff --git a/src/libstore/legacy-ssh-store.cc b/src/libstore/legacy-ssh-store.cc
index c75d50ade..ae11ca702 100644
--- a/src/libstore/legacy-ssh-store.cc
+++ b/src/libstore/legacy-ssh-store.cc
@@ -68,9 +68,9 @@ ref<LegacySSHStore::Connection> LegacySSHStore::openConnection()
     Strings command = remoteProgram.get();
     command.push_back("--serve");
     command.push_back("--write");
-    if (remoteStore.get() != "") {
+    if (std::optional rs = remoteStore.get()) {
         command.push_back("--store");
-        command.push_back(remoteStore.get());
+        command.push_back(rs->render());
     }
     conn->sshConn = master.startCommand(std::move(command));
     conn->to = FdSink(conn->sshConn->in.get());
diff --git a/src/libstore/nar-info.cc b/src/libstore/nar-info.cc
index 0d219a489..53c8a5510 100644
--- a/src/libstore/nar-info.cc
+++ b/src/libstore/nar-info.cc
@@ -1,6 +1,7 @@
 #include "globals.hh"
 #include "nar-info.hh"
 #include "store-api.hh"
+#include "json-utils.hh"
 
 namespace nix {
 
diff --git a/src/libstore/ssh-store-config.hh b/src/libstore/ssh-store-config.hh
index 09f9f23a7..841d4dbd8 100644
--- a/src/libstore/ssh-store-config.hh
+++ b/src/libstore/ssh-store-config.hh
@@ -18,7 +18,7 @@ struct CommonSSHStoreConfig : virtual StoreConfig
     const Setting<bool> compress{this, false, "compress",
         "Whether to enable SSH compression."};
 
-    const Setting<std::string> remoteStore{this, "", "remote-store",
+    const Setting<std::optional<StoreReference>> remoteStore{this, std::nullopt, "remote-store",
         R"(
           [Store URL](@docroot@/store/types/index.md#store-url-format)
           to be used on the remote machine. The default is `auto`
diff --git a/src/libstore/ssh-store.cc b/src/libstore/ssh-store.cc
index 246abaac2..41f731124 100644
--- a/src/libstore/ssh-store.cc
+++ b/src/libstore/ssh-store.cc
@@ -228,9 +228,9 @@ ref<RemoteStore::Connection> SSHStore::openConnection()
     auto conn = make_ref<Connection>();
     Strings command = remoteProgram.get();
     command.push_back("--stdio");
-    if (remoteStore.get() != "") {
+    if (std::optional rs = remoteStore.get()) {
         command.push_back("--store");
-        command.push_back(remoteStore.get());
+        command.push_back(rs->render());
     }
     command.insert(command.end(),
         extraRemoteProgramArgs.begin(), extraRemoteProgramArgs.end());
diff --git a/src/libstore/store-api.cc b/src/libstore/store-api.cc
index 7c2b3815f..8f9ec205f 100644
--- a/src/libstore/store-api.cc
+++ b/src/libstore/store-api.cc
@@ -1330,9 +1330,9 @@ std::list<ref<Store>> getDefaultSubstituters()
     static auto stores([]() {
         std::list<ref<Store>> stores;
 
-        StringSet done;
+        std::set<StoreReference> done;
 
-        auto addStore = [&](const std::string & uri) {
+        auto addStore = [&](const StoreReference & uri) {
             if (!done.insert(uri).second) return;
             try {
                 stores.push_back(openStore(uri));
diff --git a/src/libstore/store-api.hh b/src/libstore/store-api.hh
index 430d9a5ab..5bc097abf 100644
--- a/src/libstore/store-api.hh
+++ b/src/libstore/store-api.hh
@@ -863,13 +863,10 @@ OutputPathMap resolveDerivedPath(Store &, const DerivedPath::Built &, Store * ev
  */
 ref<Store> openStore(StoreReference && storeURI);
 
-
-/**
- * Opens the store at `uri`, where `uri` is in the format expected by `StoreReference::parse`
-
- */
-ref<Store> openStore(const std::string & uri = settings.storeUri.get(),
-    const Store::Params & extraParams = Store::Params());
+static inline ref<Store> openStore(const StoreReference & storeURI = settings.storeUri.get())
+{
+    return openStore(StoreReference { storeURI });
+}
 
 
 /**
diff --git a/src/libstore/store-reference.cc b/src/libstore/store-reference.cc
index b4968dfad..64a7f6287 100644
--- a/src/libstore/store-reference.cc
+++ b/src/libstore/store-reference.cc
@@ -1,4 +1,5 @@
 #include <regex>
+#include <nlohmann/json.hpp>
 
 #include "error.hh"
 #include "url.hh"
@@ -114,3 +115,22 @@ std::pair<std::string, StoreReference::Params> splitUriAndParams(const std::stri
 }
 
 }
+
+namespace nlohmann {
+
+using namespace nix;
+
+// TODO support something structured
+
+StoreReference adl_serializer<StoreReference>::from_json(const json & json)
+{
+    auto s = json.get<std::string>();
+    return StoreReference::parse(s);
+}
+
+void adl_serializer<StoreReference>::to_json(json & json, StoreReference ref)
+{
+    json = ref.render();
+}
+
+}
diff --git a/src/libstore/store-reference.hh b/src/libstore/store-reference.hh
index e99335c0d..88f35b719 100644
--- a/src/libstore/store-reference.hh
+++ b/src/libstore/store-reference.hh
@@ -4,6 +4,8 @@
 #include <variant>
 
 #include "types.hh"
+#include "json-impls.hh"
+#include "json-avoids-null.hh"
 
 namespace nix {
 
@@ -89,4 +91,14 @@ struct StoreReference
  */
 std::pair<std::string, StoreReference::Params> splitUriAndParams(const std::string & uri);
 
+/**
+ * It is always rendered as a string
+ */
+template<>
+struct json_avoids_null<StoreReference> : std::true_type
+{
+};
+
 }
+
+JSON_IMPL(StoreReference)
diff --git a/src/libstore/unix/local-overlay-store.cc b/src/libstore/unix/local-overlay-store.cc
index 598415db8..aedec9a53 100644
--- a/src/libstore/unix/local-overlay-store.cc
+++ b/src/libstore/unix/local-overlay-store.cc
@@ -26,7 +26,7 @@ LocalOverlayStore::LocalOverlayStore(const Params & params)
     , Store(params)
     , LocalFSStore(params)
     , LocalStore(params)
-    , lowerStore(openStore(percentDecode(lowerStoreUri.get())).dynamic_pointer_cast<LocalFSStore>())
+    , lowerStore(openStore(lowerStoreUri.get()).dynamic_pointer_cast<LocalFSStore>())
 {
     if (checkMount.get()) {
         std::smatch match;
diff --git a/src/libstore/unix/local-overlay-store.hh b/src/libstore/unix/local-overlay-store.hh
index 35a301013..ec6564b19 100644
--- a/src/libstore/unix/local-overlay-store.hh
+++ b/src/libstore/unix/local-overlay-store.hh
@@ -13,7 +13,7 @@ struct LocalOverlayStoreConfig : virtual LocalStoreConfig
         , LocalStoreConfig(params)
     { }
 
-    const Setting<std::string> lowerStoreUri{(StoreConfig*) this, "", "lower-store",
+    const Setting<StoreReference> lowerStoreUri{this, StoreReference{.variant = StoreReference::Auto{}}, "lower-store",
         R"(
           [Store URL](@docroot@/command-ref/new-cli/nix3-help-stores.md#store-url-format)
           for the lower store. The default is `auto` (i.e. use the Nix daemon or `/nix/store` directly).
@@ -22,12 +22,12 @@ struct LocalOverlayStoreConfig : virtual LocalStoreConfig
           Must be used as OverlayFS lower layer for this store's store dir.
         )"};
 
-    const PathSetting upperLayer{(StoreConfig*) this, "", "upper-layer",
+    const PathSetting upperLayer{this, "", "upper-layer",
         R"(
           Directory containing the OverlayFS upper layer for this store's store dir.
         )"};
 
-    Setting<bool> checkMount{(StoreConfig*) this, true, "check-mount",
+    Setting<bool> checkMount{this, true, "check-mount",
         R"(
           Check that the overlay filesystem is correctly mounted.
 
@@ -38,7 +38,7 @@ struct LocalOverlayStoreConfig : virtual LocalStoreConfig
           default, but can be disabled if needed.
         )"};
 
-    const PathSetting remountHook{(StoreConfig*) this, "", "remount-hook",
+    const PathSetting remountHook{this, "", "remount-hook",
         R"(
           Script or other executable to run when overlay filesystem needs remounting.
 
diff --git a/src/libutil/experimental-features.hh b/src/libutil/experimental-features.hh
index 1da2a3ff5..83e43c4cf 100644
--- a/src/libutil/experimental-features.hh
+++ b/src/libutil/experimental-features.hh
@@ -3,7 +3,7 @@
 
 #include "comparator.hh"
 #include "error.hh"
-#include "json-utils.hh"
+#include "json-avoids-null.hh"
 #include "types.hh"
 
 namespace nix {
diff --git a/src/libutil/json-avoids-null.hh b/src/libutil/json-avoids-null.hh
new file mode 100644
index 000000000..47f35d8b3
--- /dev/null
+++ b/src/libutil/json-avoids-null.hh
@@ -0,0 +1,57 @@
+#pragma once
+///@file
+
+#include <list>
+#include <nlohmann/json_fwd.hpp>
+
+#include "types.hh"
+
+namespace nix {
+
+/**
+ * For `adl_serializer<std::optional<T>>` below, we need to track what
+ * types are not already using `null`. Only for them can we use `null`
+ * to represent `std::nullopt`.
+ */
+template<typename T>
+struct json_avoids_null;
+
+/**
+ * Handle numbers in default impl
+ */
+template<typename T>
+struct json_avoids_null : std::bool_constant<std::is_integral<T>::value>
+{
+};
+
+template<>
+struct json_avoids_null<std::nullptr_t> : std::false_type
+{
+};
+
+template<>
+struct json_avoids_null<bool> : std::true_type
+{
+};
+
+template<>
+struct json_avoids_null<std::string> : std::true_type
+{
+};
+
+template<typename T>
+struct json_avoids_null<std::vector<T>> : std::true_type
+{
+};
+
+template<typename T>
+struct json_avoids_null<std::list<T>> : std::true_type
+{
+};
+
+template<typename K, typename V>
+struct json_avoids_null<std::map<K, V>> : std::true_type
+{
+};
+
+}
diff --git a/src/libutil/json-impls.hh b/src/libutil/json-impls.hh
index b26163a04..9dd344c50 100644
--- a/src/libutil/json-impls.hh
+++ b/src/libutil/json-impls.hh
@@ -1,7 +1,7 @@
 #pragma once
 ///@file
 
-#include "nlohmann/json_fwd.hpp"
+#include <nlohmann/json_fwd.hpp>
 
 // Following https://github.com/nlohmann/json#how-can-i-use-get-for-non-default-constructiblenon-copyable-types
 #define JSON_IMPL(TYPE)                                                \
diff --git a/src/libutil/json-utils.hh b/src/libutil/json-utils.hh
index 08c98cc8c..ea8b828f5 100644
--- a/src/libutil/json-utils.hh
+++ b/src/libutil/json-utils.hh
@@ -2,10 +2,9 @@
 ///@file
 
 #include <nlohmann/json.hpp>
-#include <list>
-#include <nlohmann/json_fwd.hpp>
 
 #include "types.hh"
+#include "json-avoids-null.hh"
 
 namespace nix {
 
@@ -39,38 +38,6 @@ Strings getStringList(const nlohmann::json & value);
 StringMap getStringMap(const nlohmann::json & value);
 StringSet getStringSet(const nlohmann::json & value);
 
-/**
- * For `adl_serializer<std::optional<T>>` below, we need to track what
- * types are not already using `null`. Only for them can we use `null`
- * to represent `std::nullopt`.
- */
-template<typename T>
-struct json_avoids_null;
-
-/**
- * Handle numbers in default impl
- */
-template<typename T>
-struct json_avoids_null : std::bool_constant<std::is_integral<T>::value> {};
-
-template<>
-struct json_avoids_null<std::nullptr_t> : std::false_type {};
-
-template<>
-struct json_avoids_null<bool> : std::true_type {};
-
-template<>
-struct json_avoids_null<std::string> : std::true_type {};
-
-template<typename T>
-struct json_avoids_null<std::vector<T>> : std::true_type {};
-
-template<typename T>
-struct json_avoids_null<std::list<T>> : std::true_type {};
-
-template<typename K, typename V>
-struct json_avoids_null<std::map<K, V>> : std::true_type {};
-
 }
 
 namespace nlohmann {
diff --git a/src/nix-copy-closure/nix-copy-closure.cc b/src/nix-copy-closure/nix-copy-closure.cc
index b64af758f..89ee63f81 100644
--- a/src/nix-copy-closure/nix-copy-closure.cc
+++ b/src/nix-copy-closure/nix-copy-closure.cc
@@ -47,7 +47,15 @@ static int main_nix_copy_closure(int argc, char ** argv)
         if (sshHost.empty())
             throw UsageError("no host name specified");
 
-        auto remoteUri = "ssh://" + sshHost + (gzip ? "?compress=true" : "");
+        StoreReference remoteUri{
+            .variant =
+                StoreReference::Specified{
+                    .scheme = "ssh",
+                    .authority = sshHost,
+                },
+            .params = gzip ? (StoreReference::Params{{"compress", "true"}}) : (StoreReference::Params{}),
+        };
+
         auto to = toMode ? openStore(remoteUri) : openStore();
         auto from = toMode ? openStore() : openStore(remoteUri);
 
diff --git a/src/nix/flake.cc b/src/nix/flake.cc
index 78a8a55c3..bdac1b4d9 100644
--- a/src/nix/flake.cc
+++ b/src/nix/flake.cc
@@ -1006,7 +1006,7 @@ struct CmdFlakeClone : FlakeCommand
 
 struct CmdFlakeArchive : FlakeCommand, MixJSON, MixDryRun
 {
-    std::string dstUri;
+    std::optional<StoreReference> dstUri;
 
     CmdFlakeArchive()
     {
@@ -1014,7 +1014,9 @@ struct CmdFlakeArchive : FlakeCommand, MixJSON, MixDryRun
             .longName = "to",
             .description = "URI of the destination Nix store",
             .labels = {"store-uri"},
-            .handler = {&dstUri}
+            .handler = {[&](std::string s) {
+                dstUri = StoreReference::parse(s);
+            }},
         });
     }
 
@@ -1075,8 +1077,8 @@ struct CmdFlakeArchive : FlakeCommand, MixJSON, MixDryRun
             traverse(*flake.lockFile.root);
         }
 
-        if (!dryRun && !dstUri.empty()) {
-            ref<Store> dstStore = dstUri.empty() ? openStore() : openStore(dstUri);
+        if (!dryRun && dstUri) {
+            ref<Store> dstStore = openStore(*dstUri);
             copyPaths(*store, *dstStore, sources);
         }
     }
diff --git a/src/nix/main.cc b/src/nix/main.cc
index bc13a4df5..667a3db17 100644
--- a/src/nix/main.cc
+++ b/src/nix/main.cc
@@ -18,6 +18,7 @@
 #include "terminal.hh"
 #include "users.hh"
 #include "network-proxy.hh"
+#include "json-utils.hh"
 
 #include <sys/types.h>
 #include <regex>
@@ -224,7 +225,7 @@ static void showHelp(std::vector<std::string> subcommand, NixArgs & toplevel)
 
     evalSettings.restrictEval = false;
     evalSettings.pureEval = false;
-    EvalState state({}, openStore("dummy://"));
+    EvalState state({}, openStore({ .variant = StoreReference::Specified { .scheme = "dummy" } }));
 
     auto vGenerateManpage = state.allocValue();
     state.eval(state.parseExprFromString(
@@ -400,7 +401,7 @@ void mainWrapped(int argc, char * * argv)
             Xp::FetchTree,
         };
         evalSettings.pureEval = false;
-        EvalState state({}, openStore("dummy://"));
+        EvalState state({}, openStore({ .variant = StoreReference::Specified { .scheme = "dummy" } }));
         auto res = nlohmann::json::object();
         res["builtins"] = ({
             auto builtinsJson = nlohmann::json::object();
diff --git a/src/nix/make-content-addressed.cc b/src/nix/make-content-addressed.cc
index d9c988a9f..dcd7860b9 100644
--- a/src/nix/make-content-addressed.cc
+++ b/src/nix/make-content-addressed.cc
@@ -30,7 +30,7 @@ struct CmdMakeContentAddressed : virtual CopyCommand, virtual StorePathsCommand,
 
     void run(ref<Store> srcStore, StorePaths && storePaths) override
     {
-        auto dstStore = dstUri.empty() ? openStore() : openStore(dstUri);
+        auto dstStore = !dstUri ? openStore() : openStore(*dstUri);
 
         auto remappings = makeContentAddressed(*srcStore, *dstStore,
             StorePathSet(storePaths.begin(), storePaths.end()));
diff --git a/src/nix/sigs.cc b/src/nix/sigs.cc
index 1e277cbbe..000a73c80 100644
--- a/src/nix/sigs.cc
+++ b/src/nix/sigs.cc
@@ -11,7 +11,7 @@ using namespace nix;
 
 struct CmdCopySigs : StorePathsCommand
 {
-    Strings substituterUris;
+    std::vector<StoreReference> substituterUris;
 
     CmdCopySigs()
     {
@@ -20,7 +20,9 @@ struct CmdCopySigs : StorePathsCommand
             .shortName = 's',
             .description = "Copy signatures from the specified store.",
             .labels = {"store-uri"},
-            .handler = {[&](std::string s) { substituterUris.push_back(s); }},
+            .handler = {[&](std::string s) {
+                substituterUris.push_back(StoreReference::parse(s));
+            }},
         });
     }
 
diff --git a/src/nix/unix/daemon.cc b/src/nix/unix/daemon.cc
index de77a7b6b..5a230f33c 100644
--- a/src/nix/unix/daemon.cc
+++ b/src/nix/unix/daemon.cc
@@ -234,10 +234,10 @@ static PeerInfo getPeerInfo(int remote)
  */
 static ref<Store> openUncachedStore()
 {
-    Store::Params params; // FIXME: get params from somewhere
+    StoreReference ref = settings.storeUri.get();
     // Disable caching since the client already does that.
-    params["path-info-cache-size"] = "0";
-    return openStore(settings.storeUri, params);
+    ref.params["path-info-cache-size"] = "0";
+    return openStore(std::move(ref));
 }
 
 /**
diff --git a/src/nix/verify.cc b/src/nix/verify.cc
index 2a0cbd19f..13c2761df 100644
--- a/src/nix/verify.cc
+++ b/src/nix/verify.cc
@@ -15,7 +15,7 @@ struct CmdVerify : StorePathsCommand
 {
     bool noContents = false;
     bool noTrust = false;
-    Strings substituterUris;
+    std::vector<StoreReference> substituterUris;
     size_t sigsNeeded = 0;
 
     CmdVerify()
@@ -37,7 +37,9 @@ struct CmdVerify : StorePathsCommand
             .shortName = 's',
             .description = "Use signatures from the specified store.",
             .labels = {"store-uri"},
-            .handler = {[&](std::string s) { substituterUris.push_back(s); }}
+            .handler = {[&](std::string s) {
+                substituterUris.push_back(StoreReference::parse(s));
+            }}
         });
 
         addFlag({
diff --git a/tests/unit/libstore-support/tests/libstore.hh b/tests/unit/libstore-support/tests/libstore.hh
index 267188224..c57bc40d8 100644
--- a/tests/unit/libstore-support/tests/libstore.hh
+++ b/tests/unit/libstore-support/tests/libstore.hh
@@ -16,7 +16,12 @@ class LibStoreTest : public virtual ::testing::Test {
 
     protected:
         LibStoreTest()
-            : store(openStore("dummy://"))
+            : store(openStore({
+                .variant = StoreReference::Specified {
+                    .scheme = "dummy",
+                    .authority = "",
+                },
+            }))
         { }
 
         ref<Store> store;