I am trying to deploy Hashicorp Vault with Kubernetes Auth Method on AWS EKS.

Hashicorp Auth Method: https://www.vaultproject.io/docs/auth/kubernetes.html

Procedure used, derived from CoreOS Vault Operator. Though I am not actually using their operator: https://github.com/coreos/vault-operator/blob/master/doc/user/kubernetes-auth-backend.md

Below is the summary of the procedure use with some additional content. Essentially, I am getting a certificate error when attempting to actually login to vault after following the needed steps. Any help is appreciated.

Create the service account and clusterrolebinding for tokenreview:

$kubectl -n default create serviceaccount vault-tokenreview

$kubectl -n default create -f example/k8s_auth/vault-tokenreview-binding.yaml

    Contents of vault-tokenreview-binding.yaml file
    =========================================
    apiVersion: rbac.authorization.k8s.io/v1beta1
    kind: ClusterRoleBinding
    metadata:
      name: vault-tokenreview-binding
      namespace: default
    roleRef:
      apiGroup: rbac.authorization.k8s.io
      kind: ClusterRole
      name: system:auth-delegator
    subjects:
    - kind: ServiceAccount
      name: vault-tokenreview
      namespace: default

Enable vault auth and add Kubernetes cluster to vault:

$SECRET_NAME=$(kubectl -n default get serviceaccount vault-tokenreview -o jsonpath='{.secrets[0].name}')
$TR_ACCOUNT_TOKEN=$(kubectl -n default get secret ${SECRET_NAME} -o jsonpath='{.data.token}' | base64 --decode)

$vault auth-enable kubernetes

$vault write auth/kubernetes/config kubernetes_host=XXXXXXXXXX kubernetes_ca_cert=@ca.crt token_reviewer_jwt=$TR_ACCOUNT_TOKEN

    Contents of ca.crt file
    NOTE: I retrieved the certificate from AWS EKS console. Which
          is shown in the "certificate authority" field in 
          base64 format. I base64 decoded it and placed it here
    =================
    -----BEGIN CERTIFICATE-----
    * encoded entry *
    -----END CERTIFICATE-----

Create the vault policy and role:

$vault write sys/policy/demo-policy policy=@example/k8s_auth/policy.hcl

    Contents of policy.hcl file
    =====================
    path "secret/demo/*" {
      capabilities = ["create", "read", "update", "delete", "list"]
    }

$vault write auth/kubernetes/role/demo-role \
    bound_service_account_names=default \
    bound_service_account_namespaces=default \
    policies=demo-policy \
    ttl=1h

Attempt to login to vault using the service account created in last step:

$SECRET_NAME=$(kubectl -n default get serviceaccount default -o jsonpath='{.secrets[0].name}')
$DEFAULT_ACCOUNT_TOKEN=$(kubectl -n default get secret ${SECRET_NAME} -o jsonpath='{.data.token}' | base64 --decode)

$vault write auth/kubernetes/login role=demo-role jwt=${DEFAULT_ACCOUNT_TOKEN}

    Error writing data to auth/kubernetes/login: Error making API request.

    URL: PUT http://localhost:8200/v1/auth/kubernetes/login
    Code: 500. Errors:

    * Post https://XXXXXXXXX.sk1.us-west-2.eks.amazonaws.com/apis/authentication.k8s.io/v1/tokenreviews: x509: certificate signed by unknown authority