add git-credential-env
and configure git to use it by default
`git-credential-env` only echoes the $GIT_CREDENTIAL_ENV environment variable
when git asks for https credentials.
with this, setting GIT_CREDENTIAL_ENV="username=name\npassword=xxx" sets the credentials
that will be used.
e.g.
docker run -e GIT_CREDENTIAL_ENV="username=name\npassword=xxx" jupyter/repo2docker
MODIFY
Dockerfile
Dockerfile
@@ -5,5 +5,6 @@ RUN apk add --no-cache git
RUN mkdir /tmp/src
ADD . /tmp/src
-RUN pip3 install --no-cache-dir /tmp/src
-
+RUN pip3 install --no-cache-dir /tmp/src && \
+ cp /tmp/src/docker/git-credential-env /usr/local/bin/git-credential-env && \
+ git config --system credential.helper env

ADD
docker/git-credential-env
+#!/bin/sh
+echo -e $GIT_CREDENTIAL_ENV

add git-credential-env

and configure git to use it by default

`git-credential-env` only echoes the $GIT_CREDENTIAL_ENV environment variable
when git asks for https credentials.

with this, setting GIT_CREDENTIAL_ENV="username=name\npassword=xxx" sets the credentials
that will be used.

e.g.

    docker run -e GIT_CREDENTIAL_ENV="username=name\npassword=xxx" jupyter/repo2docker https://github.com/private/repo