diff --git a/bridgehead b/bridgehead
index 09b46f59..499af66f 100755
--- a/bridgehead
+++ b/bridgehead
@@ -169,13 +169,21 @@ case "$ACTION" in
 	uninstall)
 		exec ./lib/uninstall-bridgehead.sh $PROJECT
 		;;
-	adduser)
+	setuser)
 		loadVars
-		log "INFO" "Adding encrypted credentials in /etc/bridgehead/$PROJECT.local.conf"
-    		read -p "Please choose the component (LDM_AUTH|NNGM_AUTH|EXPORTER_USER) you want to add a user to : " COMPONENT
-    		read -p "Please enter a username: " USER
-    		read -s -p "Please enter a password (will not be echoed): "$'\n' PASSWORD
-    		add_basic_auth_user $USER $PASSWORD $COMPONENT $PROJECT
+		log "INFO" "Setting encrypted credentials in /etc/bridgehead/$PROJECT.local.conf"
+		read -p "Please choose the component ($(echo $BASIC_AUTH_VARIABLES | tr ' ' '|')) you want to set the credentials for : " COMPONENT
+		case " $BASIC_AUTH_VARIABLES " in
+			*" $COMPONENT "*)
+				;;
+			*)
+				log "ERROR" "\"$COMPONENT\" is not a basic auth component. Choose one of: $BASIC_AUTH_VARIABLES"
+				exit 1
+				;;
+		esac
+		read -p "Please enter a username: " USER
+		read -s -p "Please enter a password (will not be echoed): "$'\n' PASSWORD
+		set_basic_auth_user "$USER" "$PASSWORD" "$COMPONENT" "$PROJECT"
 		;;
 	enroll)
 		loadVars
diff --git a/lib/check-bridgehead.sh b/lib/check-bridgehead.sh
index 57ca537c..8048b8b2 100755
--- a/lib/check-bridgehead.sh
+++ b/lib/check-bridgehead.sh
@@ -64,7 +64,29 @@ if [ "$GIT_REMOTE_OK" = true ]; then
   log INFO "Git remote connection successful."
 fi
 
-if [ "$OWNERSHIP_OK" = true ] && [ "$GIT_OK" = true ] && [ "$GIT_REMOTE_OK" = true ]; then
+# Basic auth credentials
+log INFO "Checking basic auth credentials..."
+AUTH_OK=true
+LDM_AUTH_USERS=0
+while IFS= read -r ENTRY; do
+  if is_valid_basic_auth_entry "$ENTRY"; then
+    LDM_AUTH_USERS=$((LDM_AUTH_USERS + 1))
+  else
+    log ERROR "LDM_AUTH contains the invalid entry \"$ENTRY\". Traefik rejects the whole list, leaving the local data management unreachable."
+    AUTH_OK=false
+  fi
+done < <([ -n "${LDM_AUTH:-}" ] && printf '%s\n' "$LDM_AUTH" | tr ',' '\n')
+if [ "$LDM_AUTH_USERS" -ne 1 ]; then
+  log ERROR "LDM_AUTH holds $LDM_AUTH_USERS sets of valid credentials, but exactly one is expected."
+  AUTH_OK=false
+fi
+if [ "$AUTH_OK" = true ]; then
+  log INFO "Basic auth credentials are valid."
+else
+  log INFO "Hint: Run 'bridgehead setuser $PROJECT' to replace LDM_AUTH with a single set of credentials."
+fi
+
+if [ "$OWNERSHIP_OK" = true ] && [ "$GIT_OK" = true ] && [ "$GIT_REMOTE_OK" = true ] && [ "$AUTH_OK" = true ]; then
   log INFO "All checks passed."
   exit 0
 else
diff --git a/lib/functions.sh b/lib/functions.sh
index 3a5cfe4a..57296554 100644
--- a/lib/functions.sh
+++ b/lib/functions.sh
@@ -53,7 +53,7 @@ checkOwner(){
 }
 
 printUsage() {
-	echo "Usage: bridgehead start|stop|logs|docker-logs|is-running|update|check|install|uninstall|adduser|enroll PROJECTNAME"
+	echo "Usage: bridgehead start|stop|logs|docker-logs|is-running|update|check|install|uninstall|setuser|enroll PROJECTNAME"
 	echo "PROJECTNAME should be one of ccp|bbmri|cce|itcc|kr|dhki|nngm"
 }
 
@@ -247,21 +247,55 @@ function do_enroll {
 	do_enroll_inner $@
 }
 
-add_basic_auth_user() {
-   USER="${1}"
-   PASSWORD="${2}"
-   NAME="${3}"
-   PROJECT="${4}"
-   FILE="/etc/bridgehead/${PROJECT}.local.conf"
-   ENCRY_CREDENTIALS="$(docker run --rm docker.verbis.dkfz.de/cache/httpd:alpine htpasswd -nb $USER $PASSWORD  | tr -d '\n' | tr -d '\r')"
-   if [ -f $FILE ] && grep -R -q "$NAME=" $FILE # if a specific basic auth user already exists:
-   then
-     sed -i "/$NAME/ s|='|='$ENCRY_CREDENTIALS,|" $FILE
-   else
-     echo -e "\n## Basic Authentication Credentials for:\n$NAME='$ENCRY_CREDENTIALS'" >> $FILE;
-   fi
- 	log DEBUG "Saving clear text credentials in $FILE. If wanted, delete them manually."
-   sed -i "/^$NAME/ s|$|\n# User: $USER\n# Password: $PASSWORD|" $FILE
+BASIC_AUTH_VARIABLES="LDM_AUTH NNGM_AUTH TRANSFAIR_AUTH EXPORTER_USER"
+
+# One entry of Traefik's basicauth.users list: "user:hash", with the username
+# restricted to characters that cannot collide with either separator.
+is_valid_basic_auth_entry() {
+	local entry="$1"
+	local user="${entry%%:*}"
+	local hash="${entry#*:}"
+	[ "$user" != "$entry" ] || return 1
+	[ -n "$hash" ] || return 1
+	[ "$hash" = "${hash#*:}" ] || return 1
+	[[ "$user" =~ ^[A-Za-z0-9._-]+$ ]]
+}
+
+# Stores one set of basic auth credentials in $NAME, replacing any existing ones.
+set_basic_auth_user() {
+	local USER="${1}"
+	local PASSWORD="${2}"
+	local NAME="${3}"
+	local PROJECT="${4}"
+	local FILE="/etc/bridgehead/${PROJECT}.local.conf"
+	local ENCRY_CREDENTIALS
+	if [ -z "$USER" ] || [ -z "$PASSWORD" ]; then
+		log ERROR "Both a username and a password are required. $FILE is unchanged."
+		return 1
+	fi
+	if ! ENCRY_CREDENTIALS="$(docker run --rm docker.verbis.dkfz.de/cache/httpd:alpine htpasswd -nb "$USER" "$PASSWORD")"; then
+		log ERROR "Unable to run htpasswd, so no credentials were generated. $FILE is unchanged."
+		return 1
+	fi
+	ENCRY_CREDENTIALS="$(printf '%s' "$ENCRY_CREDENTIALS" | tr -d '\n' | tr -d '\r')"
+	if ! is_valid_basic_auth_entry "$ENCRY_CREDENTIALS"; then
+		log ERROR "htpasswd returned no usable credentials for \"$USER\". $FILE is unchanged."
+		return 1
+	fi
+	if [ -f $FILE ] && grep -q "^$NAME=" $FILE # if this basic auth variable already exists:
+	then
+		sed -i "/^$NAME=/{:a;N;s/\n# User: [^\n]*//;s/\n# Password: [^\n]*//;ta}" $FILE
+		sed -i "0,/^$NAME=/!{/^$NAME=/d}" $FILE
+		sed -i "/^$NAME=/ s|=.*|='$ENCRY_CREDENTIALS'|" $FILE
+	else
+		echo -e "\n## Basic Authentication Credentials for:\n$NAME='$ENCRY_CREDENTIALS'" >> $FILE;
+	fi
+	log DEBUG "Saving clear text credentials in $FILE. If wanted, delete them manually."
+	sed -i "/^$NAME=/ s|$|\n# User: $USER\n# Password: $PASSWORD|" $FILE
+	if [ "$(grep -c "^$NAME=" $FILE)" -ne 1 ] || [ "$(sed -n "s|^$NAME='\(.*\)'$|\1|p" $FILE)" != "$ENCRY_CREDENTIALS" ]; then
+		log ERROR "$NAME in $FILE does not hold exactly one set of credentials. Please correct it manually."
+		return 1
+	fi
 }
 
 OIDC_PUBLIC_REDIRECT_URLS=${OIDC_PUBLIC_REDIRECT_URLS:-""}
diff --git a/lib/install-bridgehead.sh b/lib/install-bridgehead.sh
index 2e2ec69a..cbe6d5bd 100755
--- a/lib/install-bridgehead.sh
+++ b/lib/install-bridgehead.sh
@@ -29,29 +29,29 @@ EOF
 
 # TODO: Determine whether this should be located in setup-bridgehead (triggered through bridgehead install) or in update bridgehead (triggered every hour)
 if [ -z "$LDM_AUTH" ]; then
-  log "INFO" "Now generating basic auth for the local data management (see adduser in bridgehead for more information). "
+  log "INFO" "Now generating basic auth for the local data management (see setuser in bridgehead for more information). "
   generated_passwd="$(cat /proc/sys/kernel/random/uuid | sed 's/[-]//g' | head -c 32)"
-  add_basic_auth_user $PROJECT $generated_passwd "LDM_AUTH" $PROJECT
+  set_basic_auth_user "$PROJECT" "$generated_passwd" "LDM_AUTH" "$PROJECT"
 fi
 
 if [ ! -z "$NNGM_CTS_APIKEY" ] && [ -z "$NNGM_AUTH" ]; then
-  log "INFO" "Now generating basic auth for nNGM upload API (see adduser in bridgehead for more information). "
+  log "INFO" "Now generating basic auth for nNGM upload API (see setuser in bridgehead for more information). "
   generated_passwd="$(cat /proc/sys/kernel/random/uuid | sed 's/[-]//g' | head -c 32)"
-  add_basic_auth_user "nngm" $generated_passwd "NNGM_AUTH" $PROJECT
+  set_basic_auth_user "nngm" "$generated_passwd" "NNGM_AUTH" "$PROJECT"
 fi
 
 if [ -z "$TRANSFAIR_AUTH" ]; then
   if [[ -n "$TTP_URL" || -n "$EXCHANGE_ID_SYSTEM" ]]; then
-    log "INFO" "Now generating basic auth user for transfair API (see adduser in bridgehead for more information). "
+    log "INFO" "Now generating basic auth user for transfair API (see setuser in bridgehead for more information). "
     generated_passwd="$(cat /proc/sys/kernel/random/uuid | sed 's/[-]//g' | head -c 32)"
-    add_basic_auth_user "transfair" $generated_passwd "TRANSFAIR_AUTH" $PROJECT
+    set_basic_auth_user "transfair" "$generated_passwd" "TRANSFAIR_AUTH" "$PROJECT"
   fi
 fi
 
 if [ "$ENABLE_EXPORTER" == "true" ] && [ -z "$EXPORTER_USER" ]; then
-  log "INFO" "Now generating basic auth for the exporter and reporter (see adduser in bridgehead for more information)."
+  log "INFO" "Now generating basic auth for the exporter and reporter (see setuser in bridgehead for more information)."
   generated_passwd="$(cat /proc/sys/kernel/random/uuid | sed 's/[-]//g' | head -c 32)"
-  add_basic_auth_user $PROJECT $generated_passwd "EXPORTER_USER" $PROJECT
+  set_basic_auth_user "$PROJECT" "$generated_passwd" "EXPORTER_USER" "$PROJECT"
 fi
 
 log "INFO" "Registering system units for bridgehead and bridgehead-update"
diff --git a/lib/update-bridgehead.sh b/lib/update-bridgehead.sh
index cf846db7..5a493b38 100755
--- a/lib/update-bridgehead.sh
+++ b/lib/update-bridgehead.sh
@@ -140,9 +140,14 @@ fi
 if [ ! -z "$LDM_PASSWORD" ]; then
   FILE="/etc/bridgehead/$PROJECT.local.conf"
   log "INFO" "Migrating LDM_PASSWORD to encrypted credentials in $FILE"
-  add_basic_auth_user $PROJECT $LDM_PASSWORD "LDM_AUTH" $PROJECT
-  add_basic_auth_user $PROJECT $LDM_PASSWORD "NNGM_AUTH" $PROJECT
-  sed -i "/LDM_PASSWORD/{d;}" $FILE
+  if set_basic_auth_user "$PROJECT" "$LDM_PASSWORD" "LDM_AUTH" "$PROJECT"; then
+    if [ ! -z "$NNGM_CTS_APIKEY" ]; then
+      set_basic_auth_user "$PROJECT" "$LDM_PASSWORD" "NNGM_AUTH" "$PROJECT"
+    fi
+    sed -i "/LDM_PASSWORD/{d;}" $FILE
+  else
+    log "ERROR" "Migration failed, keeping LDM_PASSWORD in $FILE for the next attempt."
+  fi
 fi
 
 exit 0