Gradle signArchives unable to read Secret Key - gradle

Question

I am trying to publish my Java Library to Maven Central. A part of this involves using the signing gradle plugin to sign the artifacts. I need to sign it without using the keyring file as document here as I cant provide my CI secure access to the key ring file.
However when I do this my build fails with:
FAILURE: Build failed with an exception.
* What went wrong:
Could not evaluate onlyIf predicate for task ':signArchives'.
> Could not read PGP secret key
What am I doing wrong? I presume it is related to my GPG_SIGNING_KEY.
I used the full private key from the response of gpg --list-secret-keys --keyid-format LONG. Is this not correct?
My build.gradle
apply plugin: 'java'
apply plugin: 'signing'
apply plugin: 'maven'
apply from: 'publish.gradle'
sourceCompatibility = 1.8
repositories {
mavenCentral()
}
dependencies {
compile group: 'org.apache.httpcomponents', name: 'httpclient', version: '4.5.3'
testCompile 'junit:junit:4.11'
}
task Wrapper(type: Wrapper) {
gradleVersion = '5.6.2'
}
My publish.gradle
apply plugin: 'maven'
apply plugin: 'signing'
def isReleaseBuild() {
return !VERSION.contains("SNAPSHOT")
}
def getReleaseRepositoryUrl() {
return 'https://oss.sonatype.org/service/local/staging/deploy/maven2/'
}
def getSnapshotRepositoryUrl() {
return 'https://oss.sonatype.org/content/repositories/snapshots/'
}
afterEvaluate { project ->
uploadArchives {
repositories {
mavenDeployer {
beforeDeployment { MavenDeployment deployment -> signing.signPom(deployment) }
repository(url: getReleaseRepositoryUrl()) {
def ossrhUsername = OSSRH_USERNAME
def ossrhPassword = OSSRH_PASSWORD
authentication(userName: ossrhUsername, password: ossrhPassword)
}
snapshotRepository(url: getSnapshotRepositoryUrl()) {
def ossrhUsername = OSSRH_USERNAME
def ossrhPassword = OSSRH_PASSWORD
authentication(userName: ossrhUsername, password: ossrhPassword)
}
pom.groupId = GROUP_ID
pom.artifactId = ARTIFACT_ID
pom.version = VERSION
pom.project {
name ARTIFACT_ID
packaging PROJECT_PACKAGING
description PROJECT_DESCRIPTION
url PROJECT_URL
scm {
url SCM_URL
connection SCM_CONNECTION
}
licenses {
license {
name LICENSE_NAME
url LICENSE_URL
}
}
organization {
name = ORGANIZATION_NAME
url = ORGANIZATION_URL
}
developers {
developer {
id DEVELOPER_ID
name DEVELOPER_NAME
email DEVELOPER_EMAIL
}
}
}
}
}
signing {
required { isReleaseBuild() && gradle.taskGraph.hasTask("uploadArchives") }
def signingKey = GPG_SIGNING_KEY
def signingPassword = GPG_SIGNING_PASSWORD
useInMemoryPgpKeys(signingKey, signingPassword)
sign configurations.archives
}
task javadocJar(type: Jar) {
classifier = 'javadoc'
from javadoc
}
task sourcesJar(type: Jar) {
classifier = 'sources'
from sourceSets.main.allSource
}
artifacts {
archives javadocJar, sourcesJar
}
}
}
And with gradle.properties
RELEASE_REPOSITORY_URL='https://oss.sonatype.org/service/local/staging/deploy/maven2/'
SNAPSHOT_REPOSITORY_URL='https://oss.sonatype.org/content/repositories/snapshots/'
GPG_SIGNING_KEY=AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
GPG_SIGNING_PASSWORD=the password used to encrypt the key
OSSRH_USERNAME=my ossrh username
OSSRH_PASSWORD=my ossrh password
VERSION=1.0.0
GROUP_ID=com.example
ARTIFACT_ID=project-name
PROJECT_PACKAGING=...
PROJECT_DESCRIPTION=...
PROJECT_URL=...
SCM_URL=...
SCM_CONNECTION=...
LICENSE_NAME=Apache License, Version 2.0
LICENSE_URL=...
ORGANIZATION_NAME=...
ORGANIZATION_URL=...
DEVELOPER_ID=...
DEVELOPER_NAME=...
DEVELOPER_EMAIL=...

Answer 1

As you suspected, it’s the format of the secret PGP key that is wrong here. The useInMemoryPgpKeys method expects an “ascii-armored in-memory PGP secret key”. gpg --list-secret-keys is only meant for human consumption and doesn’t even show the ‘content’ of the secret key.
You can get the key in the correct format using gpg --armor --export-secret-keys foobar#example.com instead. Use your own key ID (as returned by gpg --list-secret-keys) or email address instead of foobar#example.com.
To make use of the exported key in the gradle.properties file, you need to escape the newline characters. For example, you could append a new, working line for your GPG_SIGNING_KEY property like so:
gpg --armor --export-secret-keys foobar#example.com \
| awk 'NR == 1 { print "GPG_SIGNING_KEY=" } 1' ORS='\\n' \
>> gradle.properties
(See this answer for an explanation of the main awk magic that is used here.)
With your gradle.properties file updated as described (and using your build scripts), I could successfully sign my dummy JAR files with ./gradlew signArchives.