diff --git a/docker/.env b/docker/.env
index 31a49e7..bad7172 100644
--- a/docker/.env
+++ b/docker/.env
@@ -1,11 +1,11 @@
 # This key (as well as docker-compose.yml) is only used in tests, so it's safe
 # to have it here.
-CI_STORAGE_HOST_PRIVATE_KEY_TEST_ONLY="-----BEGIN OPENSSH PRIVATE KEY-----
+CI_STORAGE_HOST_PRIVATE_KEY_EVAL_TEST_ONLY="echo '-----BEGIN OPENSSH PRIVATE KEY-----
 b3BlbnNzaC1rZXktdjEAAAAABG5vbmUAAAAEbm9uZQAAAAAAAAABAAAAMwAAAAtzc2gtZW
 QyNTUxOQAAACBZgbuAsWHfeYshNJacifV30KxJVFKr4/B4WnvxO8x2jAAAAKgm2KyUJtis
 lAAAAAtzc2gtZWQyNTUxOQAAACBZgbuAsWHfeYshNJacifV30KxJVFKr4/B4WnvxO8x2jA
 AAAECRcPB4jRqJEgNBvFPA6+k5HPT5/ZbXnD2KUyE+oJFfA1mBu4CxYd95iyE0lpyJ9XfQ
 rElUUqvj8Hhae/E7zHaMAAAAHmRtaXRyeUBEbWl0cnktTWFjQm9vay1NMS5sb2NhbAECAw
 QFBgc=
------END OPENSSH PRIVATE KEY-----"
-CI_STORAGE_HOST_PUBLIC_KEY_TEST_ONLY="ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIFmBu4CxYd95iyE0lpyJ9XfQrElUUqvj8Hhae/E7zHaM"
+-----END OPENSSH PRIVATE KEY-----'"
+CI_STORAGE_HOST_PUBLIC_KEY_EVAL_TEST_ONLY="echo 'ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIFmBu4CxYd95iyE0lpyJ9XfQrElUUqvj8Hhae/E7zHaM'"
diff --git a/docker/README.md b/docker/README.md
new file mode 100644
index 0000000..1a1ede7
--- /dev/null
+++ b/docker/README.md
@@ -0,0 +1,9 @@
+# Self Hosted Runner and ci-storage Host Container
+
+See nested README.md files.
+
+To build the containers and run/test them locally/manually:
+
+```
+./compose-up.sh
+```
diff --git a/docker/compose.yml b/docker/compose.yml
index 577c025..065dcba 100644
--- a/docker/compose.yml
+++ b/docker/compose.yml
@@ -13,7 +13,7 @@ services:
     ports:
       - 10022:22
     environment:
-      - CI_STORAGE_HOST_PUBLIC_KEY=${CI_STORAGE_HOST_PUBLIC_KEY_TEST_ONLY?}
+      - CI_STORAGE_HOST_PUBLIC_KEY_EVAL=${CI_STORAGE_HOST_PUBLIC_KEY_EVAL_TEST_ONLY?}
   self-hosted-runner:
     build:
       context: self-hosted-runner
@@ -27,4 +27,4 @@ services:
       - GH_LABELS=${GH_LABELS:-ci-storage}
       - GH_TOKEN
       - CI_STORAGE_HOST=${CI_STORAGE_HOST:-host:22}
-      - CI_STORAGE_HOST_PRIVATE_KEY=${CI_STORAGE_HOST_PRIVATE_KEY_TEST_ONLY?}
+      - CI_STORAGE_HOST_PRIVATE_KEY_EVAL=${CI_STORAGE_HOST_PRIVATE_KEY_EVAL_TEST_ONLY?}
diff --git a/docker/host/Dockerfile b/docker/host/Dockerfile
index 0513c6d..7eccabf 100644
--- a/docker/host/Dockerfile
+++ b/docker/host/Dockerfile
@@ -2,7 +2,7 @@ ARG BASE_IMAGE="ubuntu:22.04"
 
 FROM $BASE_IMAGE
 
-ENV CI_STORAGE_HOST_PUBLIC_KEY=""
+ENV CI_STORAGE_HOST_PUBLIC_KEY_EVAL=""
 
 ENV DEBIAN_FRONTEND=noninteractive
 RUN true \
diff --git a/docker/host/README.md b/docker/host/README.md
index 11e0add..cd25055 100644
--- a/docker/host/README.md
+++ b/docker/host/README.md
@@ -3,7 +3,8 @@
 Build an image from this Dockerfile to launch a simple SSH server with rsync.
 
 - Pre-creates /home/user/ci-storage directory.
-- Copies public key in CI_STORAGE_HOST_PUBLIC_KEY to user's authorized_keys.
+- Copies public key printed by `CI_STORAGE_HOST_PUBLIC_KEY_EVAL` to user's
+  authorized_keys.
 
 One "host" container may serve multiple GitHub repositories. Each of them will
 have own directory in /home/user/ci-storage (managed by ci-storage tool).
diff --git a/docker/host/entrypoint.sh b/docker/host/entrypoint.sh
index 0d3cf55..ecc0674 100644
--- a/docker/host/entrypoint.sh
+++ b/docker/host/entrypoint.sh
@@ -5,16 +5,21 @@
 #
 set -u -e
 
-if [[ "${CI_STORAGE_HOST_PUBLIC_KEY:=}" == "" ]]; then
-  echo "CI_STORAGE_HOST_PUBLIC_KEY must be set to a valid SSH public key."
+if [[ "${CI_STORAGE_HOST_PUBLIC_KEY_EVAL:=}" == "" ]]; then
+  echo "CI_STORAGE_HOST_PUBLIC_KEY_EVAL must be contain a bash script which prints a valid SSH public key (e.g. fetched from AWS Secrets Manager or so)."
   exit 1
 fi
 
-authorized_keys=~user/.ssh/authorized_keys
+authorized_keys_file=~user/.ssh/authorized_keys
+public_key=$(eval "$CI_STORAGE_HOST_PUBLIC_KEY_EVAL")
+if [[ "$public_key" == "" ]]; then
+  echo "CI_STORAGE_HOST_PUBLIC_KEY_EVAL evaluated to an empty string."
+  exit 1
+fi
 
-if [[ ! -f $authorized_keys ]] || ! grep -qF "$CI_STORAGE_HOST_PUBLIC_KEY" $authorized_keys; then
-  echo "$CI_STORAGE_HOST_PUBLIC_KEY" >> $authorized_keys
-  chown user:user $authorized_keys
+if [[ ! -f $authorized_keys_file ]] || ! grep -qF "$public_key" $authorized_keys_file; then
+  echo "$public_key" >> $authorized_keys_file
+  chown user:user $authorized_keys_file
 fi
 
 mkdir -p /var/run/sshd
diff --git a/docker/self-hosted-runner/Dockerfile b/docker/self-hosted-runner/Dockerfile
index 47d25c8..afacda5 100644
--- a/docker/self-hosted-runner/Dockerfile
+++ b/docker/self-hosted-runner/Dockerfile
@@ -7,7 +7,7 @@ ENV GH_REPOSITORY=""
 ENV GH_LABELS=""
 ENV GH_TOKEN=""
 ENV CI_STORAGE_HOST=""
-ENV CI_STORAGE_HOST_PRIVATE_KEY=""
+ENV CI_STORAGE_HOST_PRIVATE_KEY_EVAL=""
 
 ENV DEBIAN_FRONTEND=noninteractive
 RUN true \
diff --git a/docker/self-hosted-runner/root/entrypoint.00-validate.sh b/docker/self-hosted-runner/root/entrypoint.00-validate.sh
index 73bc084..0ca65b9 100644
--- a/docker/self-hosted-runner/root/entrypoint.00-validate.sh
+++ b/docker/self-hosted-runner/root/entrypoint.00-validate.sh
@@ -21,7 +21,7 @@ if [[ "${CI_STORAGE_HOST:=}" != "" && ! "$CI_STORAGE_HOST" =~ ^([-.[:alnum:]]+@)
   exit 1;
 fi
 
-if [[ "${CI_STORAGE_HOST_PRIVATE_KEY:=}" != "" && "$CI_STORAGE_HOST_PRIVATE_KEY" != *OPENSSH\ PRIVATE\ KEY* ]]; then
-  echo "If CI_STORAGE_HOST_PRIVATE_KEY is passed, it must be an SSH private key.";
+if [[ "${CI_STORAGE_HOST_PRIVATE_KEY_EVAL:=}" != "" && "$CI_STORAGE_HOST_PRIVATE_KEY_EVAL" != *\ * ]]; then
+  echo "If CI_STORAGE_HOST_PRIVATE_KEY_EVAL is passed, it must contain a shell command which prints an SSH private key (e.g. fetched from AWS Secrets Manager or so).";
   exit 1;
 fi
diff --git a/docker/self-hosted-runner/user/entrypoint.00-ci-storage-load.sh b/docker/self-hosted-runner/user/entrypoint.00-ci-storage-load.sh
index 02bf504..e02db4d 100644
--- a/docker/self-hosted-runner/user/entrypoint.00-ci-storage-load.sh
+++ b/docker/self-hosted-runner/user/entrypoint.00-ci-storage-load.sh
@@ -1,14 +1,14 @@
 #!/bin/bash
 set -u -e
 
-if [[ "$CI_STORAGE_HOST_PRIVATE_KEY" != "" ]]; then
-  echo "$CI_STORAGE_HOST_PRIVATE_KEY" > ~/.ssh/id_ed25519
+if [[ "$CI_STORAGE_HOST_PRIVATE_KEY_EVAL" != "" ]]; then
+  eval "$CI_STORAGE_HOST_PRIVATE_KEY_EVAL" > ~/.ssh/id_ed25519
   chmod 600 ~/.ssh/id_ed25519
 fi
 
 echo "$CI_STORAGE_HOST" > ci-storage-host
 
-if [[ "$CI_STORAGE_HOST" != "" && "$CI_STORAGE_HOST_PRIVATE_KEY" != "" ]]; then
+if [[ "$CI_STORAGE_HOST" != "" && "$CI_STORAGE_HOST_PRIVATE_KEY_EVAL" != "" ]]; then
   local_dir=~/actions-runner/_work/${GH_REPOSITORY##*/}/${GH_REPOSITORY##*/}
   mkdir -p "$local_dir"
   ci-storage load \