diff --git a/src/PostgREST/Config.hs b/src/PostgREST/Config.hs
index 9e07d8c41..0655641d6 100644
--- a/src/PostgREST/Config.hs
+++ b/src/PostgREST/Config.hs
@@ -43,6 +43,7 @@ data AppConfig = AppConfig {
   , configJwtSecret :: Maybe Text
   , configPool      :: Int
   , configMaxRows   :: Maybe Integer
+  , configReqCheck  :: Maybe Text
   , configQuiet     :: Bool
   }
 
@@ -57,6 +58,7 @@ argParser = AppConfig
   <*> (optional . map toS <$> strOption) (long "jwt-secret" <> short 'j' <> help "secret used to encrypt and decrypt JWT tokens" <> metavar "SECRET")
   <*> option auto  (long "pool"       <> short 'o' <> help "max connections in database pool" <> metavar "COUNT" <> value 10 <> showDefault)
   <*> (readMay <$> strOption  (long "max-rows"   <> short 'm' <> help "max rows in response" <> metavar "COUNT" <> value "infinity" <> showDefault))
+  <*> (optional . map toS . strOption) (long "pre-request"  <> help "schema-qualified name of proc to call to validate requests" <> metavar "FUNCTION")
   <*> pure False
 
 defaultCorsPolicy :: CorsResourcePolicy
diff --git a/src/PostgREST/Middleware.hs b/src/PostgREST/Middleware.hs
index 9f7e92a49..34533b23e 100644
--- a/src/PostgREST/Middleware.hs
+++ b/src/PostgREST/Middleware.hs
@@ -32,10 +32,13 @@ runWithClaims conf eClaims app req =
     JWTMissingSecret -> return $ errResponse status500 "Server lacks JWT secret"
     JWTClaims claims -> do
       -- role claim defaults to anon if not specified in jwt
-      H.sql . mconcat . claimsToSQL $ M.union claims (M.singleton "role" anon)
+      let setClaims = claimsToSQL (M.union claims (M.singleton "role" anon))
+      H.sql (mconcat $ setClaims ++ customReqCheck)
       app req
   where
     anon = String . toS $ configAnonRole conf
+    customReqCheck = maybeToList $ (\f -> "select " <> toS f <> "();")
+                                 <$> configReqCheck conf
     unauthed message = responseLBS unauthorized401
       [ ctToHeader CTApplicationJSON
       , ( "WWW-Authenticate"
diff --git a/test/Feature/AuthSpec.hs b/test/Feature/AuthSpec.hs
index 1aa586c2e..ceb2b0378 100644
--- a/test/Feature/AuthSpec.hs
+++ b/test/Feature/AuthSpec.hs
@@ -103,6 +103,11 @@ spec = describe "authorization" $ do
           ]
         }
 
+  it "runs a custom request validation proc" $ do
+    let auth = authHeaderJWT "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJyb2xlIjoiYmFkX3JvbGUifQ.ENAiheEOlskpfoT5byj-gKJkOhHKTvETQu1Zso3c4Ts"
+    request methodGet "/items" [auth] ""
+      `shouldRespondWith` 400
+
   it "should fail when jwt contains no claims" $ do
     let auth = authHeaderJWT "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.e30.lu-rG8aSCiw-aOlN0IxpRGz5r7Jwq7K9r3tuMPUpytI"
     request methodGet "/authors_only" [auth] ""
diff --git a/test/SpecHelper.hs b/test/SpecHelper.hs
index c4a800ceb..b07ffe225 100644
--- a/test/SpecHelper.hs
+++ b/test/SpecHelper.hs
@@ -51,23 +51,23 @@ testDbConn = "postgres://postgrest_test_authenticator@localhost:5432/postgrest_t
 
 testCfg :: AppConfig
 testCfg =
-  AppConfig testDbConn "postgrest_test_anonymous" Nothing "test" "localhost" 3000 (Just "safe") 10 Nothing True
+  AppConfig testDbConn "postgrest_test_anonymous" Nothing "test" "localhost" 3000 (Just "safe") 10 Nothing (Just "test.block_bad_role") True
 
 testCfgNoJWT :: AppConfig
 testCfgNoJWT =
-  AppConfig testDbConn "postgrest_test_anonymous" Nothing "test" "localhost" 3000 Nothing 10 Nothing True
+  AppConfig testDbConn "postgrest_test_anonymous" Nothing "test" "localhost" 3000 Nothing 10 Nothing Nothing True
 
 testUnicodeCfg :: AppConfig
 testUnicodeCfg =
-  AppConfig testDbConn "postgrest_test_anonymous" Nothing "تست" "localhost" 3000 (Just "safe") 10 Nothing True
+  AppConfig testDbConn "postgrest_test_anonymous" Nothing "تست" "localhost" 3000 (Just "safe") 10 Nothing Nothing True
 
 testLtdRowsCfg :: AppConfig
 testLtdRowsCfg =
-  AppConfig testDbConn "postgrest_test_anonymous" Nothing "test" "localhost" 3000 (Just "safe") 10 (Just 2) True
+  AppConfig testDbConn "postgrest_test_anonymous" Nothing "test" "localhost" 3000 (Just "safe") 10 (Just 2) Nothing True
 
 testProxyCfg :: AppConfig
 testProxyCfg =
-  AppConfig testDbConn "postgrest_test_anonymous" (Just "https://postgrest.com/openapi.json") "test" "localhost" 3000 (Just "safe") 10 Nothing True
+  AppConfig testDbConn "postgrest_test_anonymous" (Just "https://postgrest.com/openapi.json") "test" "localhost" 3000 (Just "safe") 10 Nothing Nothing True
 
 setupDb :: IO ()
 setupDb = do
diff --git a/test/fixtures/privileges.sql b/test/fixtures/privileges.sql
index 3a94812af..fa590df9f 100644
--- a/test/fixtures/privileges.sql
+++ b/test/fixtures/privileges.sql
@@ -4,7 +4,7 @@ GRANT USAGE ON SCHEMA
     , test
     , jwt
     , "تست"
-TO postgrest_test_anonymous;
+TO postgrest_test_anonymous, bad_role;
 
 -- Schema test objects
 SET search_path = test, "تست", pg_catalog;
diff --git a/test/fixtures/roles.sql b/test/fixtures/roles.sql
index a146a8fc8..aa507c87d 100644
--- a/test/fixtures/roles.sql
+++ b/test/fixtures/roles.sql
@@ -1,7 +1,8 @@
-DROP ROLE IF EXISTS postgrest_test_authenticator, postgrest_test_anonymous, postgrest_test_default_role, postgrest_test_author;
+DROP ROLE IF EXISTS postgrest_test_authenticator, postgrest_test_anonymous, postgrest_test_default_role, postgrest_test_author, bad_role;
 CREATE ROLE postgrest_test_authenticator WITH login noinherit;
 CREATE ROLE postgrest_test_anonymous;
 CREATE ROLE postgrest_test_default_role;
 CREATE ROLE postgrest_test_author;
+CREATE ROLE bad_role;
 
-GRANT postgrest_test_anonymous, postgrest_test_default_role, postgrest_test_author TO postgrest_test_authenticator;
+GRANT postgrest_test_anonymous, postgrest_test_default_role, postgrest_test_author, bad_role TO postgrest_test_authenticator;
diff --git a/test/fixtures/schema.sql b/test/fixtures/schema.sql
index 42356ce9a..56d8f6d8e 100755
--- a/test/fixtures/schema.sql
+++ b/test/fixtures/schema.sql
@@ -237,6 +237,14 @@ SELECT jwt.sign(
   ) r;
 $$;
 
+create function block_bad_role() returns void
+language plpgsql as $$
+begin
+  if current_role = 'bad_role' then
+    raise invalid_password using message = 'role is not allowed';
+  end if;
+end
+$$;
 
 --
 -- Name: reveal_big_jwt(); Type: FUNCTION; Schema: test; Owner: -