diff --git a/Cargo.lock b/Cargo.lock
index 632c22b..bec683e 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -45,9 +45,9 @@ dependencies = [
 
 [[package]]
 name = "anyhow"
-version = "1.0.45"
+version = "1.0.48"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "ee10e43ae4a853c0a3591d4e2ada1719e553be18199d9da9d4a83f5927c2f5c7"
+checksum = "62e1f47f7dc0422027a4e370dd4548d4d66b26782e513e98dca1e689e058a80e"
 
 [[package]]
 name = "ascii"
@@ -289,9 +289,9 @@ checksum = "ccaeedb56da03b09f598226e25e80088cb4cd25f316e6e4df7d695f0feeb1403"
 
 [[package]]
 name = "crc32fast"
-version = "1.2.1"
+version = "1.2.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "81156fece84ab6a9f2afdb109ce3ae577e42b1228441eded99bd77f627953b1a"
+checksum = "3825b1e8580894917dc4468cb634a1b4e9745fddc854edad72d9c04644c0319f"
 dependencies = [
  "cfg-if",
 ]
@@ -406,9 +406,9 @@ dependencies = [
 
 [[package]]
 name = "futures"
-version = "0.3.17"
+version = "0.3.18"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a12aa0eb539080d55c3f2d45a67c3b58b6b0773c1a3ca2dfec66d58c97fd66ca"
+checksum = "8cd0210d8c325c245ff06fd95a3b13689a1a276ac8cfa8e8720cb840bfb84b9e"
 dependencies = [
  "futures-channel",
  "futures-core",
@@ -421,9 +421,9 @@ dependencies = [
 
 [[package]]
 name = "futures-channel"
-version = "0.3.17"
+version = "0.3.18"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "5da6ba8c3bb3c165d3c7319fc1cc8304facf1fb8db99c5de877183c08a273888"
+checksum = "7fc8cd39e3dbf865f7340dce6a2d401d24fd37c6fe6c4f0ee0de8bfca2252d27"
 dependencies = [
  "futures-core",
  "futures-sink",
@@ -431,9 +431,9 @@ dependencies = [
 
 [[package]]
 name = "futures-core"
-version = "0.3.17"
+version = "0.3.18"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "88d1c26957f23603395cd326b0ffe64124b818f4449552f960d815cfba83a53d"
+checksum = "629316e42fe7c2a0b9a65b47d159ceaa5453ab14e8f0a3c5eedbb8cd55b4a445"
 
 [[package]]
 name = "futures-enum"
@@ -448,9 +448,9 @@ dependencies = [
 
 [[package]]
 name = "futures-executor"
-version = "0.3.17"
+version = "0.3.18"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "45025be030969d763025784f7f355043dc6bc74093e4ecc5000ca4dc50d8745c"
+checksum = "7b808bf53348a36cab739d7e04755909b9fcaaa69b7d7e588b37b6ec62704c97"
 dependencies = [
  "futures-core",
  "futures-task",
@@ -470,18 +470,16 @@ dependencies = [
 
 [[package]]
 name = "futures-io"
-version = "0.3.17"
+version = "0.3.18"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "522de2a0fe3e380f1bc577ba0474108faf3f6b18321dbf60b3b9c39a75073377"
+checksum = "e481354db6b5c353246ccf6a728b0c5511d752c08da7260546fc0933869daa11"
 
 [[package]]
 name = "futures-macro"
-version = "0.3.17"
+version = "0.3.18"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "18e4a4b95cea4b4ccbcf1c5675ca7c4ee4e9e75eb79944d07defde18068f79bb"
+checksum = "a89f17b21645bc4ed773c69af9c9a0effd4a3f1a3876eadd453469f8854e7fdd"
 dependencies = [
- "autocfg",
- "proc-macro-hack",
  "proc-macro2",
  "quote",
  "syn",
@@ -489,23 +487,22 @@ dependencies = [
 
 [[package]]
 name = "futures-sink"
-version = "0.3.17"
+version = "0.3.18"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "36ea153c13024fe480590b3e3d4cad89a0cfacecc24577b68f86c6ced9c2bc11"
+checksum = "996c6442437b62d21a32cd9906f9c41e7dc1e19a9579843fad948696769305af"
 
 [[package]]
 name = "futures-task"
-version = "0.3.17"
+version = "0.3.18"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "1d3d00f4eddb73e498a54394f228cd55853bdf059259e8e7bc6e69d408892e99"
+checksum = "dabf1872aaab32c886832f2276d2f5399887e2bd613698a02359e4ea83f8de12"
 
 [[package]]
 name = "futures-util"
-version = "0.3.17"
+version = "0.3.18"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "36568465210a3a6ee45e1f165136d68671471a501e632e9a98d96872222b5481"
+checksum = "41d22213122356472061ac0f1ab2cee28d2bac8491410fd68c2af53d1cedb83e"
 dependencies = [
- "autocfg",
  "futures-channel",
  "futures-core",
  "futures-io",
@@ -515,8 +512,6 @@ dependencies = [
  "memchr",
  "pin-project-lite",
  "pin-utils",
- "proc-macro-hack",
- "proc-macro-nested",
  "slab",
 ]
 
@@ -819,9 +814,9 @@ checksum = "e2abad23fbc42b3700f2f279844dc832adb2b2eb069b2df918f455c4e18cc646"
 
 [[package]]
 name = "libc"
-version = "0.2.107"
+version = "0.2.108"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "fbe5e23404da5b4f555ef85ebed98fb4083e55a00c317800bc2a50ede9f3d219"
+checksum = "8521a1b57e76b1ec69af7599e75e38e7b7fad6610f037db8c79b127201b5d119"
 
 [[package]]
 name = "libsqlite3-sys"
@@ -1169,18 +1164,6 @@ dependencies = [
  "version_check",
 ]
 
-[[package]]
-name = "proc-macro-hack"
-version = "0.5.19"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "dbf0c48bc1d91375ae5c3cd81e3722dff1abcf81a30960240640d223f59fe0e5"
-
-[[package]]
-name = "proc-macro-nested"
-version = "0.1.7"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "bc881b2c22681370c6a780e47af9840ef841837bc98118431d4e1868bd0c1086"
-
 [[package]]
 name = "proc-macro2"
 version = "1.0.32"
@@ -1421,9 +1404,9 @@ dependencies = [
 
 [[package]]
 name = "serde_json"
-version = "1.0.70"
+version = "1.0.72"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e277c495ac6cd1a01a58d0a0c574568b4d1ddf14f59965c6a58b8d96400b54f3"
+checksum = "d0ffa0837f2dfa6fb90868c2b5468cad482e175f7dad97e7421951e663f2b527"
 dependencies = [
  "indexmap",
  "itoa",
@@ -1660,9 +1643,9 @@ dependencies = [
 
 [[package]]
 name = "syn"
-version = "1.0.81"
+version = "1.0.82"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f2afee18b8beb5a596ecb4a2dce128c719b4ba399d34126b9e4396e3f9860966"
+checksum = "8daf5dd0bb60cbd4137b1b587d2fc0ae729bc07cf01cd70b36a1ed5ade3b9d59"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -2157,9 +2140,9 @@ dependencies = [
 
 [[package]]
 name = "whoami"
-version = "1.2.0"
+version = "1.2.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "c33ac5ee236a4efbf2c98967e12c6cc0c51d93a744159a52957ba206ae6ef5f7"
+checksum = "524b58fa5a20a2fb3014dd6358b70e6579692a56ef6fce928834e488f42f65e8"
 dependencies = [
  "wasm-bindgen",
  "web-sys",
diff --git a/src/graphql.rs b/src/graphql.rs
index 0eacde9..3b1913e 100644
--- a/src/graphql.rs
+++ b/src/graphql.rs
@@ -136,6 +136,28 @@ fn is_valid_user_name(username: &str) -> bool {
     true
 }
 
+async fn user_authentication(db: &SqlitePool, user: &uuid::adapter::Simple, password_hash: &str) -> FieldResult<()> {
+    if sqlx::query(format!(
+        r#"SELECT users.id FROM users, security_preferences WHERE users.id = "{}" AND password_hash = "{}""#,
+        user,
+        password_hash,
+    ).as_str()).fetch_optional(db).await?.is_some() {
+        Ok(())
+    } else {
+        Err("authentication failed".into())
+    }
+}
+
+async fn user_exists(db: &SqlitePool, user: &uuid::adapter::Simple) -> FieldResult<()> {
+        if sqlx::query(
+            format!(r#"SELECT id FROM users WHERE id = "{}""#, user).as_str()
+        ).fetch_optional(db).await?.is_some() {
+            Ok(())
+        } else {
+            Err(format!(r#"user "{}" does not exist on this server"#, user).into())
+        }
+}
+
 #[derive(Clone, Debug)]
 pub struct Context {
     #[cfg(feature = "sqlite")]
@@ -529,14 +551,7 @@ impl Mutation {
         let users = BTreeSet::from_iter([user, chat_partner]);
 
         // User authentication
-        let authentication_successful = sqlx::query(format!(
-            r#"SELECT users.id FROM users, security_preferences WHERE users.id = "{}" AND password_hash = "{}""#,
-            user,
-            password_hash,
-        ).as_str()).fetch_optional(&context.db).await?.is_some();
-        if !authentication_successful {
-            return Err("authentication failed".into());
-        }
+        user_authentication(&context.db, &user, &password_hash).await?;
 
         // Chat partner needs to be another user (for now)
         if user == chat_partner {
@@ -544,12 +559,7 @@ impl Mutation {
         }
 
         // Chat partner must exist
-        let chat_partner_exists = sqlx::query(
-            format!(r#"SELECT id FROM users WHERE id = "{}""#, chat_partner).as_str()
-        ).fetch_optional(&context.db).await?.is_some();
-        if !chat_partner_exists {
-            return Err(format!(r#"chat partner "{}" does not exist on this server"#, chat_partner).into());
-        }
+        user_exists(&context.db, &chat_partner).await?;
 
         // non-group chats must be unique
         let chat_already_exists = sqlx::query(format!(