cmd/tsidp: add README and Dockerfile (#15205)

cmd/tsidp/Dockerfile

@@ -0,0 +1,41 @@
+# Build stage
+FROM golang:alpine AS builder
+
+# Install build dependencies
+RUN apk add --no-cache git
+
+# Set working directory
+WORKDIR /src
+
+# Copy only go.mod and go.sum first to leverage Docker caching
+COPY go.mod go.sum ./
+RUN go mod download
+
+# Copy the entire repository
+COPY . .
+
+# Build the tsidp binary
+RUN go build -o /bin/tsidp ./cmd/tsidp
+
+# Final stage
+FROM alpine:latest
+
+# Create necessary directories
+RUN mkdir -p /var/lib/tsidp
+
+# Copy binary from builder stage
+COPY --from=builder /bin/tsidp /app/tsidp
+
+# Set working directory
+WORKDIR /app
+
+# Environment variables
+ENV TAILSCALE_USE_WIP_CODE=1 \
+    TS_HOSTNAME=tsidp \
+    TS_STATE_DIR=/var/lib/tsidp
+
+# Expose the default port
+EXPOSE 443
+
+# Run the application
+ENTRYPOINT ["/app/tsidp"]