The easiest way from the command line:

echo "This is my secret" | base64 | read output;kubectl patch secret my_secret_name -p="{\"data\":{\"secret_key\": \"$output\"}}" -v=1

It will encode value This is my secret and update your my_secret_name secret by adding secret_key key and encoded values as a last key-value pair in that secret.

The fastest way I found:

# You need a version of micro that includes this commit https://github.com/zyedidia/micro/commit/9e8d76f2fa91463be660737d1de3bff61258c90d
kubectl get secrets my-secret -o json | jq -r .data.config | base64 -d | micro | base64 -w 0 | xclip -selection clipboard && kubectl edit secrets my-secret

The most direct (and interactive) way should be to execute kubectl edit secret <my secret>. Run kubectl get secrets if you'd like to see the list of secrets managed by Kubernetes.

As I found myself in the need of modifying a secret, I landed up here.

Here is the most convenient way I found for editing a (one-line) secret.

This elaborates on kubectl edit secret <my secret> of Timo Reimann above.

kubectl edit secret <my secret> will (in my case) invoke vi.

Now I move the cursor to the space after the colon of the secret I want to edit.

Then I press r and [enter] which will put the base64 encoded value onto a line of its own.

Now I enter :. ! base64 -D which will decode the current line.

After making my changes to the value, I enter :. ! base64 which will encode the changed value.

Pressing k [shift]J will rejoin the secret name and its new value.

:wq will write the new secretfile and quit vi.

P.S. If the secret has a multi-line value, switch on line numbers (:set nu) and, after changing the decoded value, use A,B ! base64 where A and B are the line numbers of the first and last line of the value.

P.P.S I just learned the hard way that base64 will receive the text to encode with an appended newline :( If this is no issue for your values - fine. Otherwise my current solution is to filter this out with: .!perl -pe chomp | base64

In case you prefer a non-interactive update, this is one way of doing it:

kubectl get secret mysecret -o json | jq '.data["foo"]="YmFy"' | kubectl apply -f -

Note that YmFy is a base64-encoded bar string. If you want to pass the value as an argument, jq allows you to do that:

kubectl get secret mysecret -o json | jq --arg foo "$(echo bar | base64)" '.data["foo"]=$foo' | kubectl apply -f -

I'm more comfortable using jq but yq should also do the job if you prefer yaml format.

Deriving from 'Skeeves' answer:

Base64 encode your value:
echo -n 'encode_My_Password' | base64
Open the secret in edit mode:
kubectl edit secret my-secret

The default editor will open, replace the value of an exiting key or add a new line and a new key with the encoded value. Save and close the file. The updated value or new key-value pair has now been added to the secret.

I implemented a kubectl plugin just for this.

To install using krew

kubectl krew update
kubectl krew install modify-secret

To run it

kubectl modify-secret xyz -n kube-system

Demo

<img src="https://github.com/rajatjindal/kubectl-modify-secret/raw/master/demo/usage.gif" alt="using kubectl-modify-secret plugin" style="max-width:100%;">