diff --git a/apisix/plugins/openid-connect.lua b/apisix/plugins/openid-connect.lua
index 054cc6f1b1d5..612d61c8f454 100644
--- a/apisix/plugins/openid-connect.lua
+++ b/apisix/plugins/openid-connect.lua
@@ -1322,6 +1322,27 @@ function _M.rewrite(plugin_conf, ctx)
                 return 302
             end
 
+            -- Transient authorization error from the identity provider: the ID
+            -- provider redirected to the redirect_uri with
+            -- error=temporarily_unavailable instead of a code, e.g. Keycloak's
+            -- login session expiring before the user completed authentication.
+            -- This is recoverable, so restart the authentication flow by
+            -- sending the browser back to the original URL instead of
+            -- dead-ending with a 500. Other error codes (access_denied,
+            -- login_required, ...) are not retried here, since they reflect a
+            -- deliberate outcome rather than a transient failure.
+            local uri_args = ngx.req.get_uri_args()
+            if uri_args.error == "temporarily_unavailable" and target_url
+               and ngx.req.get_method() == "GET" then
+                core.log.warn("OIDC authorization callback reported a temporarily ",
+                              "unavailable identity provider",
+                              uri_args.error_description and
+                                  (" (" .. uri_args.error_description .. ")") or "",
+                              ", restarting the authentication flow")
+                core.response.set_header("Location", target_url)
+                return 302
+            end
+
             core.log.error("OIDC authentication failed: ", err)
             return 500
         end
diff --git a/t/plugin/openid-connect12.t b/t/plugin/openid-connect12.t
new file mode 100644
index 000000000000..2be22bc86c83
--- /dev/null
+++ b/t/plugin/openid-connect12.t
@@ -0,0 +1,201 @@
+#
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You under the Apache License, Version 2.0
+# (the "License"); you may not use this file except in compliance with
+# the License.  You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+use t::APISIX 'no_plan';
+
+log_level('debug');
+repeat_each(1);
+no_long_string();
+no_root_location();
+
+add_block_preprocessor(sub {
+    my ($block) = @_;
+
+    if (!defined $block->request) {
+        $block->set_value("request", "GET /t");
+    }
+
+    # every block here drives resty.openidc into an error path on purpose,
+    # which logs at [error]; assert on the specific message instead
+    if ((!defined $block->error_log) && (!defined $block->no_error_log)) {
+        $block->set_value("no_error_log", "no such assertion");
+    }
+});
+
+run_tests();
+
+__DATA__
+
+=== TEST 1: create a route protected by openid-connect
+--- config
+    location /t {
+        content_by_lua_block {
+            local t = require("lib.test_admin").test
+            local code, body = t('/apisix/admin/routes/oidc12',
+                 ngx.HTTP_PUT,
+                 [[{
+                        "uri": "/oidc12/*",
+                        "plugins": {
+                            "openid-connect": {
+                                "client_id": "apisix",
+                                "client_secret": "secret",
+                                "discovery": "http://127.0.0.1:8080/realms/basic/.well-known/openid-configuration",
+                                "redirect_uri": "http://127.0.0.1:1984/oidc12/callback",
+                                "ssl_verify": false,
+                                "session": {
+                                    "secret": "6S8IO+A+6KJsdazbjNyG7g=="
+                                }
+                            }
+                        },
+                        "upstream": {
+                            "nodes": {
+                                "127.0.0.1:1980": 1
+                            },
+                            "type": "roundrobin"
+                        }
+                }]]
+            )
+            if code >= 300 then
+                ngx.status = code
+            end
+            ngx.say(body)
+        }
+    }
+--- response_body
+passed
+
+
+
+=== TEST 2: a callback reporting a temporarily unavailable IDP restarts the flow
+--- config
+    location /t {
+        content_by_lua_block {
+            local http = require "resty.http"
+            local base = "http://127.0.0.1:" .. ngx.var.server_port
+
+            local function cookie_of(res)
+                local c = res.headers["Set-Cookie"]
+                if type(c) == "table" then
+                    c = table.concat(c, "; ")
+                end
+                return c and c:match("^([^;]+)")
+            end
+
+            -- start a login flow and keep the session cookie
+            local res_a = http.new():request_uri(base .. "/oidc12/page")
+            local state = res_a.headers["Location"]:match("state=([^&]+)")
+            local jar = cookie_of(res_a)
+
+            -- the ID provider redirects back with an error instead of a code,
+            -- e.g. the user's login session expired at the IDP
+            local res_b = http.new():request_uri(
+                base .. "/oidc12/callback?error=temporarily_unavailable" ..
+                    "&error_description=authentication_expired&state=" .. state, {
+                    headers = {Cookie = jar}
+                })
+            ngx.say(res_b.status, " ", tostring(res_b.headers["Location"]))
+        }
+    }
+--- response_body
+302 /oidc12/page
+--- error_log
+restarting the authentication flow
+
+
+
+=== TEST 3: a callback with a different IDP error still fails with 500
+--- config
+    location /t {
+        content_by_lua_block {
+            local http = require "resty.http"
+            local base = "http://127.0.0.1:" .. ngx.var.server_port
+
+            local function cookie_of(res)
+                local c = res.headers["Set-Cookie"]
+                if type(c) == "table" then
+                    c = table.concat(c, "; ")
+                end
+                return c and c:match("^([^;]+)")
+            end
+
+            local res_a = http.new():request_uri(base .. "/oidc12/page")
+            local state = res_a.headers["Location"]:match("state=([^&]+)")
+            local jar = cookie_of(res_a)
+
+            -- access_denied reflects a deliberate outcome, not a transient
+            -- failure, so it must not be silently retried
+            local res_b = http.new():request_uri(
+                base .. "/oidc12/callback?error=access_denied" ..
+                    "&error_description=user+denied+access&state=" .. state, {
+                    headers = {Cookie = jar}
+                })
+            ngx.say(res_b.status)
+        }
+    }
+--- response_body
+500
+
+
+
+=== TEST 4: a non-GET callback reporting a temporarily unavailable IDP still fails with 500
+--- config
+    location /t {
+        content_by_lua_block {
+            local http = require "resty.http"
+            local base = "http://127.0.0.1:" .. ngx.var.server_port
+
+            local function cookie_of(res)
+                local c = res.headers["Set-Cookie"]
+                if type(c) == "table" then
+                    c = table.concat(c, "; ")
+                end
+                return c and c:match("^([^;]+)")
+            end
+
+            local res_a = http.new():request_uri(base .. "/oidc12/page")
+            local state = res_a.headers["Location"]:match("state=([^&]+)")
+            local jar = cookie_of(res_a)
+
+            local res_b = http.new():request_uri(
+                base .. "/oidc12/callback?error=temporarily_unavailable" ..
+                    "&error_description=authentication_expired&state=" .. state, {
+                    method = "POST",
+                    body = "",
+                    headers = {Cookie = jar}
+                })
+            ngx.say(res_b.status)
+        }
+    }
+--- response_body
+500
+
+
+
+=== TEST 5: a callback reporting a temporarily unavailable IDP without a session cookie still fails with 500
+--- config
+    location /t {
+        content_by_lua_block {
+            local http = require "resty.http"
+            local base = "http://127.0.0.1:" .. ngx.var.server_port
+            local res = http.new():request_uri(
+                base .. "/oidc12/callback?error=temporarily_unavailable" ..
+                    "&error_description=authentication_expired&state=deadbeef")
+            ngx.say(res.status)
+        }
+    }
+--- response_body
+500